Occasional Papers Museum of Texas Tech University Number 209 9 July 2001 A Comparison of the Flora of Northern Padre Island TO THAT OF MATAGORDA ISLAND, MUSTANG ISLAND and Southern Padre Island, Texas Allan Nelson, Jim Goetze, and Adam Lucksinger The Texas Coast is bordered by a series of bar¬ rier islands floristically similar to other barrier islands of the Gulf and Atlantic Coasts except that upland sites on Texas barrier islands often grade into extensive grassland areas (Judd et al., 1977; Duncan and Duncan, 1987; Britton and Morton, 1989). Texas barrier is¬ lands were formed by deposition of sand during the Pleistocene and, as sea levels fluctuated, island physi¬ ography changed (McAlister and McAlister, 1993). Annual temperatures increase and annual precipitation decreases from north to south down the Texas coast (McAlister and McAlister, 1993). Typical habitats found on Texas barrier islands include coppice dunes, foredunes, barrier flats, and tidal flats (Nelson et al., 2000 ). Padre Island National Seashore (PrNS) encom¬ passes most of northern Padre Island (Figure 1) and has recently been examined for fl oris tic composition (Negrete et al., 1999). Matagorda Island represents the northernmost barrier island (Figure 1) in this in¬ vestigation and has been previously examined for flo¬ ral composition (McAlister and McAlister, 1993). Corpus Christi Pass once separated northern Padre Island from Mustang Island but this pass is now filled and the two islands are joined (Wei se and White, 1980). Nonetheless, the flora of Mustang Island is consid¬ ered separately from that of northern Padre Island (Gillespie, 1976; Jones, 1982). Southern Padre Island is considered separately from northern Padre Island in floristic analyses (Judd et al., 1977; Lonard et al., 197 8; Lonard and Judd, 1980) and is physically separated from northern Padre Island by the Mansfield Ship Channel (Figure 1). The purpose of this investigation is to compare the most recent floristic inventory of PINS (Negrete et al., 1999) to three other barrier island systems along the southeastern Texas coast. Northern Padre Island is compared to other Texas barrier islands in terms of community similarity, percentage of shared and unique taxa, endangered and threatened species, as well as endemism and richness in relation to island areas. In addition, an inter-island checklist of known flora of some major barrier islands of Texas is provided to aid conservation managers. 2 Occasional Papers, Museum of Texas Tech University Nueces Co, Highway 35 Texa^ x Mexico 16 km Figure 1. Map of the barrier islands of Texas (hatched lines indicate the boundaries of Padre Island National Seashore). Inset shows the southernmost islands along the Texas coast (modified from Weise & White 1980). Nelson et al.— Comparison of Flora of Barrier Islands, Texas 3 Methods and Materials Data from Matagorda Island (McAlister and McAlister, 1993), Mustang Island (Gillespie, 1976; Jones, 1982), northern Padre Island (Negrete et al., 1999), and southern Padre Island (Lonard et al., 1978; Lonard and Judd, 1980) were compiled and used in flonstic comparisons. Nomenclature of native or natu¬ ralized plants was standardized using Jones et ah (1997). Numbers of species, genera, and families from each barrier island were used to calculate richness, percentages of common familes, and coefficients of community (Lonard et al., 1978; Brower et al., 1990). Coefficients of community (CC) were calculated by CC= 2c/s,+ s 2 , where s, and s 2 are the number of species in the island communities 1 and 2, respec¬ tively, and c is the number of species common to both island communities (Lonard et al., 1978). Putative endemism was determined using data from Correll and Johnston (1970), Amos (1991), Lonard and Judd (1980), Britton and Morton (1989), and Carr and Diamond (1995). Island area was taken from published sources (McAlister and McAlister, 1993) or was determined using polygon measurements on 1:100,000 scale maps in Terrain Navigator, Edition 1.0 (Anonymous, 1998). Z-values were calculated using the equation S = CA Z , where S is the number of species on the island, A is island area, and C and Z are constants. The exponent Z determines the slope of the curve and is referred to as a Z value (MacArthur and Wilson, 1967). Coefficients of determination (r 2 ) were calculated between richness and endemism com¬ pared to island areas. Results All barrier islands shared 32 families, 78 genera, and 84 species (Table 1). A number of taxa were limited to each of the four barrier islands. Northern Padre Island had 10 families 54 genera, and 172 spe¬ cies limited to the island (Table 2). Matagorda Island had 11 families, 38 genera and 68 species that are lim¬ ited, whereas Mustang Island had no families, ten gen¬ era, and 18 species (Table 2). Southern Padre Island had two families, 11 genera, and 34 species that are limited to the island (Table 2). Thirty-one species that are endemic to Texas are found on these barrier is¬ lands (Table 1) and two species may be endemic to Gulf barrier islands (Lonard and Judd, 1980; Britton and Morton, 1989). Matagorda Island has 13, Mus¬ tang Island has 11, northern Padre Island has 24, and southern Padre Island has five species endemic to the state (Table 1). The richest flora was found on north¬ ern Padre Island, whereas Mustang Island has the few¬ est taxa (Table 2). Thirteen families comprised greater than two-thirds of species found on these islands (Table 3). Families Asteraceae, Fabaceae, and Poaceae com¬ prised greater than 40% of species on the islands (Table 3) . Asteraceae comprised the greatest proportion of species on Matagorda Island, Fabaceae on Mustang Island, and Poaceae on northern and southern Padre islands (Table 3). Coefficients of community for spe¬ cies, genera, and families indicated northern Padre Is¬ land and Matagorda Island were most similar (Table 4) . Mustang Island was most similar to Matagorda Island in terms of species and generic composition, but was more similar to northern Padre Island in terms of family composition (Table 4). However, it had the lowest coefficient of community for species compared to northern Padre Island (Table 4). Southern Padre Island had the lowest coefficients of community for genera and families in inter-island comparisons (Table 4) . The Z value for species richness was 0.453 and for endemism was 0,654 (Table 5). Species richness and endemism were correlated with island area (Table 5 ) . Table I. Presence (+) or absence (-) oftaxa in the floras of Matagorda Island , Mustang Island, northern Padre Island , and southern Padre Island. Texas endemic species are in boldfaced italics. Common names, when available, are given in parentheses and follow Correll and Johnston (1970), Taxon/common name ” Matagorda Mustang rr. Padre s. Padre Taxon/common name Matagorda Mustang n. Padre s. Padre 4 Occasional Papers, Museum of Texas Tech University + 4 - + + + + + + + + + + + + + + +.+ ... i + + + + + + + 111111111111+1++1 + + + + + + .+ + + + + + , 4 - 4 - 4 - ... . + . i i. + + + + 4 - + + , 1 . 4 - 4 - 4 - + + + + + + + + + + + + + + + + + + + 4 - 4 - + . . . . . . . . .+ .+ + +> ... + |+ + + + + + -{- , + . + + + + ,4- + + I+ + + + + + + + + + + + + + + + + + ,+ + + + + + + i + + + + + + + + + + i + + + + i < < + + + , * + + + + + Si .£ Table L coni ____________ Taxon/common name Matagorda Mustang n. Padre s Padre Taxor/common name Matagorda Mustang n. Padre s. Padre Nelson et al.-— Comparison of Flora of Barrier Islands, Texas 5 +.. . . . . i + 1 ■ .+ < !+•+.+ < j+i+i+i i t i t i 1 + 4- + + + + + + + + + i + .+ + + + + + + . ,+ + + + + + + + + . - .+ + + + + + .+ + ' + . 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S 0 s c : ^ 2 5, « i 3 3 i s > o H tl) u C u G ^ ►o? >**; >**; --, *-, ^ = ■» U O ■c E? -5 Gl o : 1 | ^ e § !is« v o 1 « g; E « ”3 | 3 .E pc; t/1 oj it D, « ^ E 4J &o 1 - 3 TD (X 13 (Si O iso ? g D 4J c ^ -c J X £ ^ s (J 3 E x 3 » *S 5 j? o ■‘ c ? b « » to a > w 3 b x « c - G t«j BE ?3 0) Ou = B g_Q_2 ! 13 £ 1 -B -2 ; g-b: 1 a 8 | , ^ 3 ^ 2 b 5 . o 3 Table L cont. ________.__ Taxon/common name Matagorda Mustang n. Padre s. Padre Taxon/common name Matagorda Mustang n. Padre s. 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Comparative studies of species composition allow examination of unique components of the flora, endemism, and r i chne ss. Community coe ffic i ents pro - vide a quantitative means to compare similarity of taxa among barrier islands. In addition, common elements of barrier island flora can be discerned and biogeo- graphic hypotheses proposed. Fl oral endemism of each barrier island Flaveria brownii and Sporobolus tharpii were thought to occur only on Padre Island and on barrier islands off the coast of Tamaulipas (Lonard and Judd, 1980; Britton and Morton, 1989). Flaveria brownii is frequent on brackish, low grounds (Jones, 1982) and is often found in barrier flats on northern Padre Island in the fall (Nelson et al., 1999). However, it has been observed on all four barrier islands included in this investigation (Asteraceae, Table 1) and thus occurs further north than originally reported. Sporobolus tharpii is morphologically similar to the widespread species S. wrightii (Lonard and Judd, 1980) and needs to be examined taxonomically. Herein, S. tharpii (Poaceae, Table 1) is reported from Matagorda Island, northern Padre Island, and southern Padre Island. It is usually found on sand and calcareous shell soils (Gould and Box, 1965). Although few endemic plants occur on the west¬ ern barrier islands of the Gulf of Mexico, a number of possible Texas state endemic species occur on the barrier islands included in this investigation (Table 1). The greatest numbers of species endemic to the state <> £ + + .+ .+ .++++ + i + + + + + + + + ,+ + ,+ .+ + + + + + + , ,+ + + + + + + + ,+ + + + + + + + + + + + + + +i+i+« i + + i i i ++++++ - + . . .+ + + . .+.++.++++++ + + + + + + + + + + + + + + + + + ■o - c c "T (J O o Er nj C U c ~ ° P 2 'O W ^ C s = a ss 4> "S3 p =! ca S3 s= S3 * X 0 u 4J 3 ™ “ , C > • u " _ g w o < - S op > s 'M. e C & s 3 - CTJ C _ is C C x £3 p d Co H 4) w 4) O _ efl ft « " 3 « S5 V. (4 sj .w p 53 ^ E a i> B ^3 » t; c^.s ° 3 '§ « t I £ S’ t*. '7i K X k. -3 (3 _ t o - -i; « * £ ■5 = £ 5. a .5- ** £ -5 < s g & 5 £ E e ^ ‘ ■Ei o =3 £ a 3 Oo i. U CS “53 ?! §. A « (u S 5 « 5 a ‘5 £ £ 53 P C4 « Q g > « « ? S S' w « ^ t, C c ‘S y 1) P (j « I 53 o to to to &- 1 E—< t—i E-J ^ t—i E « 5 (3 £ = * ^ =3 ^ £ e oj ^ p ^ B ^ > & & c 3 ri bo g: !- k « 53 C 3 a n i3 3 c c s" £ « B ‘7 & s ® Ml « g a ™ 53 "55 O |i M in E I ■“ _ a v c 5J 3 5* & 53 kj ^ a, n; ^ 53 (4 vT5 ^ 5 2 3 > 0 u o ti O. _ 1> s If v — 'S rt ' !S O y i » ^ a w a> £ .S3 sit a* y „ S Q, l. _3 o 3 M 1 5! 7 N ^ K 14 Occasional Papers, Museum of Texas Tech University Table 2 . Number of plant species, genera, and families reported from Matagorda Island, Mustang Island, north¬ ern Padre Island, and southern Padre Island. Numbers of each taxon limited to particular islands are given in parentheses . Species Genera Families Matagorda 299 (68) 217(38) 72(11) Mustang 183(18) 157(10) 51(0) northern Padre 456(172) 259 (54) 77(10) southern Padre 216(34) 160(11) 48 (2) Table 3. Percentages ofspecies of the most common fami¬ lies based on the total number of species present on each island. Family Matagorda Mustang n. Padre s. Padre Amaranthaceac 1.3% 2.2% 2.0% 1.9% Asteraceae 14.0% 13,1% 12.5% 13.0% Chenopodiaceae 2.7% 2.7% 2,4% 3.2% Convolvulaceae 2.0% 2,2% 1.0% 1.0% Cyperaceae 4.3% 2.7% 6 4% 5.6% Euphorbiaceae 2.7% 5.5% 4.2% 3.2% Fabaceae 9.7% 14,2% 9.4% 11,6% Juncaceae 2.0% 0.0% 1.8% 0.0% Malvaceae 3.0% 2,7% 1.5% 1.0% Onagraceae 2.7% 2.2% 2.0% 2.8% Poaceae 16.4% 13.7% 20.8% 25.5% Scrop h u 1 an aceae 2.0% 2.7% 2.9% 3.2% Soianaccae 2.0% 1.6% 1.3% 2.3% Others 35.2% 34,5% 31.8% 25.7% (24) are found on northern Padre Island (Table 5). All endemic species present on northern Padre Island will be discussed in this section. Tradescantia humilis (Commelinaceae, Table 1) is locally abundant in sandy soils in shady areas (Jones, 1982), and also has been observed on Mustang and northern Padre islands. Four grasses (Poaceae, Table 1) endemic to the state are found on northern Padre Island. Digitaria texana is known only from sandy areas of the middle and lower Gulf Coast (Gould and Box, 1965; Hatch et al. f 1999) and has been observed on northern and southern Padre islands as well as Matagorda Island. Panicum nodatum is occasionally found in sandy soils of the middle and lower Gulf Coast, whereas Tridens congestus is scattered in poorly drained, clay soils and saline, marshy grasslands bor¬ Table 4. Coefficients of Community for species, genera, and families for pairwise comparisons of floral commu¬ nity similarity between Matagorda Island, Mustang Is¬ land, northern Padre Island and southern Padre Island. Species. Matagorda Mustang n. Padre s. Padre Matagorda Mustang north Padre — 53.1% 56.1% 47.6% 50.5% 49.1% 50.0% Genera: Matagorda Mustang n. Padre s. Padre Matagorda — 66.3% 70,6% 61.5% Mustang — 65,9% 61,8% north Padre — — 65.9% Familes: Matagorda Mustang n. Padre s. Padre Matagorda —— 71.5% 79.2% 66.7% Mustang —- —- 78,1% 70,7% north Padre —- —— — 70.4% Table 5. Relationship between species richness and is¬ land size as well as number of endemics and island size . Island Area (km 1 ) Species Richness No. of Endemics Matagorda 146.35 299 13 Mustang 64.84 183 I 1 northern Padre 272.20 456 24 southern Padre 56.03 216 5 z-valu 0.453 0.654 r 1 (vs, area) 0.833 0,697 dering the Gulf (Gould and Box, 1965; Hatch et ai, 1999). Both have only been observed on northern Padre Island (Negrete et al., 1999). Vaseyochloa multinervosa is locally abundant on sandy sites of the lower and middle Gulf Coast (Hatch, 1999) and has been observed on both northern and southern Padre islands. The Aizoaceae, Boraginaceae, Brassicaceae, Capparadaceae, Fumariaceae, Oxalidaceae, and Plantaginaceae each contain a single endemic found on northern Padre Island (Table 1). Sesuvium trianthemoides was thought to be fairly frequent in brackish swales, marshes, and depressions along the coast (Jones, 1982). However most of these occur¬ rences were based upon misidentified specimens and the only known, extant population (personal commu- Nelson et al.— Comparison of Flora of Barrier Islands, Texas 15 nication with B. Carr of the Nature Conservancy) has been observed on northern Padre Island (Negrete et al., 1999). Heliotropium racemosum is rather frequent on deep sands (Jones, 1982) and occurs on Mustang and northern Padre Islands. Lepidium lasiocarpum is widely scattered on deep sands along the coast (Jones, 1982). Polanisia erosa occurs in deep sands from Aransas National Wildlife Refuge to Baffm Bay (Jones, 1982). Both species have only been observed on north¬ ern Padre Island. Corydalis micrantha var. texensis is frequently found on various soils in prairies, openings, fields, and disturbed areas (Jones, 1982) and is found on Mustang and northern Padre islands. Oxalis drummondii is common in pastures, woods, stream edges, and disturbed areas (Jones, 1982). Plantago hookeriana is frequent in sandy soils of prairies, open¬ ings, and waste places (Jones, 1982). Both occur on all the barrier islands in this investigation except south¬ ern Padre Island. However, they have been reported from the mainland adjacent to southern Padre Island (Richardson, 1995), Six species of Asteraceae occur on northern Padre Island and are endemic to Texas (Table 1). Helianthus praecox ssp. runyonii is frequently found on coastal sands (Jones, 1982) and occurs only on northern Pa¬ dre Island. Two species of Palafoxia are endemic to the state and primarily occur near the coast (Jones, 1982). Palafoxia hookeriana has been observed on northern Padre and Matagorda islands whereas P. rosea var. rosea is known only from northern Padre Island. Senecio riddellii is frequent on deep coastal sands (Jones, 1982) and has been observed on northern Pa¬ dre and Matagorda islands, Tetragonotheca repanda occupies habitats similar to S . riddellii (Jones, 1982), but is known from Mustang and northern Padre is¬ lands. Thelesperma nuecense is frequent on deep coastal sands (Jones, 1982) and has been observed only on northern Padre Island. Three species of Euphorbiaceae are found on northern Padre Island and are endemic to Texas (Table 1). Croton coryi is localized on the foredunes of northern Padre Island (Jones, 1982) while C. parksii is local¬ ized on deep sands in prairies and openings along the coast and farther inland (Jones, 1982), and is found on both Mustang and northern Padre islands. Euphor¬ bia innocua is frequent on deep sands in openings, prairies, and on dunes (Jones, 1982) of Mustang and northern Padre islands. Two species of Fabaceae are endemic to the state and found on northern Padre Island. Da lea obovata is frequent on coastal sands and occasionally occurs inland (Jones, 1982). It only has been observed on northern Padre Island. Galactia canescens has been observed on Matagorda, Mustang, and northern Padre islands and has been reported from counties adjacent to southern Padre Island (Richardson, 1995). It is frequent in sandy areas near the coast and island dunes (Jones, 1982). Matagorda Island has 13 species that are endemic to Texas (Table 1). Eight of these have been previ¬ ously discussed. The remaining five species are found only on Matagorda Island. Yucca tenuis tyla occurs south of the Edwards Plateau to the south-central coast of Texas (Correll and Johnston, 1970). Tradescantia subacaulis occurs locally on looser sands in openings and prairies (Jones, 1982). Herbertia lahue is fre¬ quently found on sand or clay soils in prairies and open¬ ings (Jones, 1982). Bromus texensis occurs infre¬ quently (Jones, 1982) and often grows in the protec¬ tion of shrubs in sandy loam soils found in the middle and upper portions of the Texas coast (Hatch, 1999). Cucurbita texana is rare (Correll and Johnston, 1970) and usually occurs along rivers and bayshores (Jones, 1982). Mustang Island has 11 species endemic to the state, and southern Padre Island has five (Table 1). In both cases, all but one of these species has been dis¬ cussed previously. Lesquerella grandiflora (Brassicaceae, Table 1) has been observed only on Mustang Island. It is occasionally found in southern and central Texas in sandy soils of prairies and open¬ ings (Correll and Johnston, 1970; Jones, 1982). Core¬ opsis nuecensis (Asteraceae, Table 1) is rather com¬ mon on sandy loam in prairies (Jones, 1982) and has been observed only on southern Padre Island. It has not been reported from the adjacent mainland (Richardson, 1995) and was rare in disturbed sites near roads on the island (Lonard et al,, 1978). 16 Occasional Papers, Museum of Texas Tech University Taxa limited to each barrier island A number of taxa are limited to each of the four barrier islands. More taxa are limited to northern Pa¬ dre Island than to the other three barrier islands. Nine of the ten families limited to northern Padre Island are associated with aquatic habitats. Two of these fami¬ lies are comprised of submerged, marine aquatic spe¬ cies. Cymodocea jiliformis and Halodule beaudettei (Cymodoceaceae, Table 1) are frequent to common in Laguna Madre and bay waters (Jones, 1982) but have not been reported from the other barrier barrier is¬ lands. Halophila engelmannii and Thalassia testudinum (Hydrocharitaceae, Table 1) are found in most bays along the Texas coast (Jones, 1982). Seven additional families, each represented by a single species, are associated with freshwater habi¬ tats. Drosera brevifolia (Droseraceae, Table 1) is car¬ nivorous and occurs occasionally on moist sands on northern Padre Island and in similar habitats scattered along the adjacent mainland (Jones, 1982). Elatine triandra (Elatinaceae, Table 1) occurs frequently along the coast on damp or low grounds in shallow water or mud (Jones, 1982). Utricularia subulata (Lentibulariaceae, Table 1) is carnivorous with subter¬ ranean branches and underground bladders or traps (Cornell and Johnston, 1970). It is locally abundant in moist sands of swales along the coast (Jones, 1982). Morelia cerifera (Myricaceae, Table 1) is frequent on coastal sands (Jones, 1982) and often occurs along streams, lakes, in boggy grasslands, and wet wood¬ lands (Conell and Johnston, 1970). Lepuropetalon spathulatum (Saxifragaceae, Table 1) is localized on damp sandy or clayey soils (Jones, 1982). Najas guadalupensis (Najadaceae, Table 1) is frequent in ponds, marshes, lakes, and ditches (Jones, 1982). Xyris jupicai (Xyridaceae, Table 1) occurs in moist sandy soils or depressions on northern Padre Island (Jones, 1982). The large number of unique, aquatic families on northern Padre Island can be accounted for by numerous marshes that occur throughout the barrier flats along its length (Nelson et ah, 1999). Only two species (in family Cistaceae, Table 1) limited to northern Padre Island do not occur in aquatic habitats. Helianthemum georgianum is frequent in sandy oak woods along the coast and Lechea mucronata is frequent on sandy soils in prairies and openings (Jones, 1982). Most species limited to northern Padre Island occur in sandy soils, are widely scattered and have small population sizes, and many are ruder al, as re¬ ported for the flora of southern Padre Island (Lonard et al., 1978). However, about 30% of species limited to northern Padre Island are associated with aquatic habitats. Two unique grass species, Sorghastrum nutans andH ndropogon gerardii indicate that habitats are recovering from grazing that occurred there from 1850 to 1971. Sorghastrum nutans is found only in well managed areas and both S. nutans and A , gerardii are part of the coastal prairie climax ecosystem (Hatch, 1999). These species often occur with Schizachrium scoparium var. littoralis, which dominates the barrier flat habitat on most of northern Padre Island (Nelson et al., 1999). Matagorda Island has the second largest number of limited taxa (Table 1). Two of these families (Potamogetonaceae and Zannichelliaceae, Table 1) are freshwater aquatics and are each represented by a single species. Potamogeton pectinatus and Zannichellia palustris are rare along the middle Texas coast (Jones, 1982). The remainder of the families limited to Matagorda Island are part of a well devel¬ oped shell ridge community that occurs on the bay- side margin of Matagorda Island that is high enough in elevation to support thick, woody cover (McAlister and McAlister, 1993). Seven families are each repre¬ sented by a single woody species. Ilex vomitoria (Aquifoliaceae, Table, I) is common in sandy oak woods (Jones, 1982). Diospyros texana (Ebenaceae, Table 1) is common on various soils in mottes, brushy pastures, and woods (Jones, 1982). Elaeagnus angustifolia (Elaegnaceae, Table 1) likely escaped from cultivation on the island. Maclura pomifera (Moraceae) is relatively rare along the middle Texas coast, whereas Fores tier a angustifolia (Oleaceae, Table 1) is com¬ mon on various soils in pastures and woods (Jones, 1982). Sideroxylon celastrinum (Sapotaceae, Table 1) occurs in sandy and clayey loams sometimes contain¬ ing shell, mostly in brushy thickets along ravines and bluffs near the coast (Jones, 1982). Celtis pallida (Ulmaceae, Table 1) is common on various soils in brushy pastures and is scattered in prairie habitats Nelson et al.— Comparison of Flora of Barrier Islands, Texas 17 (Jones, 1982). Two additional families, the Rhamnaceae and Rosaceae (Table 1), are comprised of five woody species limited to Matagorda Island. Condalia hookeri and Ziziphus obtusifolia are com¬ mon on various soils in brushy pastures and C. hookeri is occasionally found along streams and in woods (Jones, 1982). Prunus caroliniana, a popular orna¬ mental in the eastern one-third of Texas, occurs in and on the edge of forests, lowland areas, fields, and thick¬ ets of eastern Texas (Correll and Johnston, 1970). Rosa bracteata is native to China and is associated with stream lowlands, swales, and along ditches (Jones, 1982). It is often planted as a living fence and readily escapes from cultivation (Correll and Johnston, 1970). Rubrus riograndis is almost ubiquitous as a weedy plant occurring in various soil types (Correll and Johnston, 1970) and is common along streams and occasional along ravines and in coastal woods (Jones, 1982). Of the taxa limited to Matagorda Island, many are associated with sandy soils, occur in small popula¬ tions, and are ruderal. There are fewer aquatic habi¬ tats (about 24%) than on northern Padre Island (about 30%) and thus fewer species are limited to these habi¬ tats. However, the chief difference is the woody un¬ derstory species. This category contains about 38% of the species limited to Matagorda Island. Of the four barrier islands, Matagorda Island contains the larg¬ est woody element in its flora. On southern Padre Island, the two families lim¬ ited to the island each contain a single species. Schinus terebinthifolius (Anacardiaceae, Table 1) is an intro¬ duced ornamental (Correll and Johnston, 1970). Clematis drummondii (Ranunculaceae, Table 1) is com¬ mon on sandy and clayey loam or caliche in pastures and woods (Jones, 1982). Most of the genera and species limited to south¬ ern Padre Island prefer sandy soils, are widely scat¬ tered with small population sizes, and are ruderal, as was reported for the flora of southern Padre Island when compared to Mustang Island (Lonard et ah, 1978). There is less of an aquatic element (estimated at about 18% of limited taxa) than on either northern Padre Island or Matagorda Island. About 15% of the limited genera and species likely escaped from cultiva¬ tion and became naturalized on the island. Taxa limited to Mustang Island follow a pattern similar to southern Padre Island (Lonard et al., 1978) with many sand-loving ruderals that are widely scat¬ tered, have small population sizes, and are escaped from cultivation. Mustang Island has the fewest spe¬ cies associated with aquatic habitats (estimated at about 11 %). Species richness, endemism, and island biogeographv The richest flora is found on northern Padre Is¬ land, whereas Mustang Island contains the fewest taxa (Table 2). Much of the floral diversity found on the islands is due to the presence of ruderal weedy spe¬ cies and the patchy occurrence of other invading spe¬ cies. In addition, most of the genera limited to south¬ ern Padre Island or Mustang Island are represented by a single species (Lonard et al., 1978). On Matagorda, Mustang, and southern Padre islands, 47-50% of the familes are represented by a single species, whereas only 30% of the families found on northern Padre Is¬ land are comprised of a single species. All the genera limited to Mustang and southern Padre islands are rep¬ resented by a single species, 97.4% of the genera lim¬ ited to Matagorda Island are represented by a single species, and 92.6% of the genera limited to northern Padre Island are represented by a single species. Species richness and endemism on Texas bar¬ rier islands are correlated with island area (r 2 values in Table 5). Results of our study generally agree with island biogeography models proposed by Mac Arthur and Wilson (1967). Larger islands usually support more species than smaller ones and, when plotted on a double log scale, the number of species increases linearly with island size according to the equation S = CA*. The exponent Z determines the slope of the curve and is referred to as a Z value (Table 5). Whenever consid¬ ering a variety of taxa on many different island sys¬ tems, Z values have been found to range from 0.24 to 0.33 (MacArthur and Wilson, 1967). When species richness and endemism was plotted against island area in this investigation, the islands had Z values of 0,453 and 0.654, respectively (Table 5). MacArthur and Wilson (1967) attribute larger values to topographic diversity, proximity to the mainland, and rates of im¬ migration and extinction. There is little topographic diversity on the islands with the exception of greater 18 Occasional Papers, Museum of Texas Tech University numbers of wetland habitats on northern Padre Is¬ land. High rates of immigration could occur on is¬ lands close to the mainland and, for the islands in this investigation, distance from the mainland is often less than 2.0 km. Because there is little difference in dis¬ tance from the mainland among the four islands, this factor would not greatly influence species richness or endemism. Extinctions on the islands would likely be caused by anthropogenic disturbances, tropical storms, hurricanes, or droughts. Island biogeography theory predicts that extinctions should be greatest on smaller islands. With similar topography and rates of immi¬ gration among the islands, extinction likely has the greatest influence on the Z values. Greater extinction rates on smaller islands (south¬ ern Padre and Mustang islands) could result in higher than normal Z values. It should be noted that human development on the smaller islands is greater than on Matagorda and northern Padre islands, which also could contribute to extinctions on the smaller islands. High Z values may also occur when studying only a few islands (MacArthur and Wilson, 1967). As the Texas barrier island floras are analyzed in detail, this initial Z value may decrease with larger sample sizes. Island colonization from the mainland is com¬ mon but mainland floras are more diverse. Lonard and Judd (1980) found that 44% of species on south¬ ern Padre Island also occurred on the adjacent main¬ land at Laguna Atascosa National Wildlife Refuge, Lonard and Judd (1980) estimated that about twice as many species occurred on Laguna Atasccosa National Wildlife Refuge and McAlister and McAlister (1993) estimated that Aransas National Wildlife Refuge, adja¬ cent to Matagorda Island, supports about three times as many species as the island. If one combines the floras of northern Padre and Mustang islands, there are 485 species on the island complex compared to 1411 species reported by Jones (1982) for an area covering a large portion of the adjacent mainland. In all cases, the island floras are depauparate in compari¬ son to the adjacent mainland floras. Community Coefficients The coefficients of similarity (Table 4) indicate that the northern islands are more similar to each other than to southern Padre Island. This is likely due to the north-south temperature and rainfall gradient along the islands. Southern Padre Island has the driest and warm¬ est climate of the four barrier islands examined in this investigation. The subtropical climate of southern Pa¬ dre Island is apparent in its flora, with 28% of its na¬ tive species having tropical affinities (Lonard et ah, 1980). Patterns could also be influenced by the amount of floristic information available for each island. Differences in community similarity between is¬ lands are largely influenced by species that occur on two or three of the islands. Of thel36 species shared between pairs of islands (Table 1), 41.2% are shared between Matagorda and northern Padre islands, 27.9% between northern and southern Padre islands, 16.2% between northern Padre and Mustang islands, 5.8 % between Matagorda and southern Padre islands, and less than 5% for other combinations of islands. Matagorda and northern Padre islands share 56 spe¬ cies, 23 of which probably do not occur on southern Padre Island based on known distributions. Fimbristylis caroliniana (Cyperaceae), Sisyrinchium sagittiferum (Iridaeeae), Juncus bufonis, J. megacephalus, J. roemerianus, J. validus (Juncaceae), Cynanchum angustifolium (Asclepidaceae), Helianthus debilis, Palafoxia hookeriana (Asteraceae), Opuntia stricta (Cactaceae), Ipomoea sagittata (Convolvulaceae), Glottidium vesicara, Strophostyles leiosperma (Fabaceae), Mentzelia oligosperma (Loasaceae), Gaura longiflora, Ludwigia glandulosa (Onagraceae), Polygala verticillata (Polygalaceae), Zanthoxylum clava-herculis, Z. hirsutum (Rutaceae), Agalinusfasiculata (Scrophulariaceae), and Parietaria floridana (Urticaceae) (Table 1) are not known from Cameron, Hidalgo, or Willacy counties (Richardson, 1995) of the adjacent mainland. Panicum acuminatum , and Sphenopholis obtusata (Poaceae, Table 1) are not known to occur along the southernmost Texas coast (Hatch, 1999). Mustang and northern Padre islands share 24 species, eight of which would not likely oc¬ cur on southern Padre Island based on known distri¬ butions, Tradescantia humilis (Commelinaceae), Froelichia floridana (Amaranthaceae), Iva imbricata (Asteraceae), Heliotropium convolvulaceum, //. racemosum (Boraginaceae), Euphorbia innocua (Euphorbiaceae), Plantago virginica (Plantaginaceae), and Phlox glabriflora are not known from Cameron, Hidalgo, or Willacy counties (Richardson, 1995) of the mainland. Matagorda and Mustang islands share Nelson et al.— Comparison of Flora of Barrier Islanos, Texas 19 six species that could occur on northern and southern Padre Islands. Northern Padre, Matagorda, and Mustang islands each share species with southern Padre Island. North¬ ern and southern Padre islands share 38 species. These species also could occur on Matagorda and Mustang islands. Matagorda and southern Padre islands share eight species, whereas Mustang and southern Padre islands share four species. In both cases, these spe¬ cies could also occur on northern Padre Island. Eighty-two species are shared by three islands (Table 1) and are referred to as triplets. The largest numbers of triplets (47.6%) exclude Mustang Island. Based on known distributions, all these species could occur on Mustang Island but do not. This may be due to its small area or relative lack of floristic sampling compared to the other islands. Southern Padre Island is excluded 41.5% of the time from the triplet cat¬ egory (Table 1) and 11 of these species probably do not occur on southern Padre Island based on known mainland distributions (Richardson, 1995; Hatch, 1999). Excluded species include Cyperus surinamensis (Cyperaceae), Panicum aciculare (Poaceae), Centella asiatica, Hydrocotyl umbellata (Apiaceae), Cirsium horridulum, Helianthus argophyllus, Thelesperma filifolium (Asteraceae), Euphorbia maculata (Euphorbiaceae), Stylosanthes viscosa (Fabaceae), Kosteletzkya virginiana (Malvaceae), Oxalis dillenii (Oxalidaceae), and Tamarix gallica (Tamaricaceae) (Table 1). Matagorda Island is excluded from the trip¬ let category in 9,8% of the cases whereas Northern Padre Island is excluded 1.2% of the time. The exclu¬ sion of these islands does not appear to be due to dis¬ tribution, as all the species in this category could po¬ tentially occur on all four islands. A number of spe¬ cies in the triplet category are regarded as common, frequent, or abundant (Jones, 1982; Hatch, 1999) and, though not reported, could occur on islands that are excluded and would comprise part of the common flora of the islands. Common flora of the islands Thirteen families comprise greater than two- thirds of the species found on the four barrier islands (Table 3). Of the 84 common (occurring on all four islands) species (Table 1), only one, Flaveria brownii , is endemic and none of the common flora is consid¬ ered endangered or threatened by the Texas Organiza¬ tion for Endangered Species. Most of the common flora is native, but 4.8 % is introduced. Cynodon dactylon (Poaceae) is native to Eurasia and found throughout Texas but is abundant in coastal areas (Correll and Johnston, 1970) in low moist sites (Jones, 1982). It is also tolerant of saline soils (Jones, 1982) which has undoubtedly aided its establishment on the barrier islands, Sonchus oleraceus is an European introduction found throughout the state (Correll and Johnston, 1970) and Is frequent on vari¬ ous soils in fields, waste places, prairies, and openings (Jones, 1982). Melilotus indicus (Fabaceae) is native to Eurasia and is common in waste places and along roads (Jones, 1982). Richardia brasiliensis is native to South America and occurs on dunes, in coastal prai¬ ries and sandy scrub oak areas as well as roadsides and waste places (Correll and Johnston, 1970). Most of the flora common to the barrier islands is herbaceous to sub-shrubby, with only 3.6% of the species being shrubs or trees. This lack of woody vegetation is unique to Texas barrier islands and was noted for southern Padre Island (Judd et al, 1977). The pronounced lack of woody vegetation is not char¬ acteristic of barrier islands further south along the Mexican coastline (Britton and Morton, 1989). The small component of the common woody flora includes; Opuntia engelmannii (Cactaceae), Acacia minuata, Prosopis glandulosa (Fabaceae), and Lycium carolinianum (Solanaceae, Table 1). All Texas barrier islands are considered part of the Gulf Prairies and Marshes biome (Correll and Johnston, 1970) and much of the islands' common flora is comprised of grasses (Poaceae) and other marsh plants. Grasses comprise 17% of the common flora whereas plants that occur in marshy habitats com¬ prise 24% of the common flora. Plants that comprise the common flora of marshy habitats on the barrier islands include: Cyperus retrorsus, Eleocharis montevidensis t Rhynchospora colorata, Schoenoplectus pungens (Cyperaceae), Andropogon glomeratus , Monanthochloe littoralis, Spartinapatens, S. spartinae, Sporobolus virginicus (Poaceae), Hydrocotyle 20 Occasional Papers, Museum of Texas Tech University bonariensis (Apiaceae), Borrichia frutescens , Conoclinium betonicifolium, Flaveria brownii, Pluchea purpurascens (Asteraceae), Batis maritima (Bataceae), Salicornia bigelovii (Chenopodiaceae), Sesbania exaltata (Fabaceae), Limonium carolinianum (Plumbaginaceae), Samolus ebracteatus (Primulaceae), and Bacopa monnieri (Scrophulariaceae). Common flora also occur in coppice dune, foredune, barrier flat, tidal flat, and disturbed habitats as identified by Nelson et al. (1999) in the Big Ball Hill region of northern Padre Island (Figure 1). Previous researchers also designated habitat types for the is¬ lands (Judd et al, 1977; Lonard et al, 1978; Lonard and Judd, 1981; Jones, 1982), These designations will provide some information on the types and diversity of habitats where the common flora is found. The fewest members of the common flora are found in coppice dune habitats and include Sporobolus virginicus, Uniola paniculata (Poaceae), Sesuvium poriulacastrum (Aizoaceae), Tidestromia lanuginosa (Amaranthaceae), Heterotheca subaxillaris (Asteraceae), Cakile lanceolata (Brass icaeeae), Ipo - moea imperati, I, pescaprae (Convolvulaceae), and Croton punctatus (Euphorbiaceae). Foredune and tidal flat habitats share an almost equal number of common floral species (16 and 14 respectively). Common flora that occur in the foredune habitat include: Paspalum monostachyum , P. setaceum , Sporobolus virginicus, Uniola paniculata (Poaceae), Sesuvium poriulacastrum (Aizoaceae), Tides tromia lanuginosa (Amaranthaceae), Asclepias oenofheroides (Asclepidaceae), Heterotheca subaxillaris (Asteraceae), Polypremum procumbens (Buddlejaceae), Opuntia engelmannii (Cactaceae), Ipomoea imperati, L pes¬ caprae (Convolvulaceae), Croton punctatus (Euphorbiaceae), Chamaecrista fasiculata, Indigofera miniata (Fabaceae), and Oenothera drummondii (Onagraceae) (Table 1), Species of the common flora that occur in the tidal flat include: Schoenoplectus pungens (Cyperaceae), Monanthochloe littoralis, Spartina patens , Sporobolus virginicus (Poaceae), Blutaparon vermiculare (Amaranthaceae), Borrichia frutescens , Iva texensis , Machaeranthera phyllocephala (Asteraceae), Batis maritima (Bataceae), Heliotropium curas savicum (Boraginaceae), Saticomia bigelovii, Suaeda linearis (Chenopodiaceae), Limonium carolinianum (Plumbaginaceae), and Lycium carolinianum (Solanaceae). Greatest numbers of the common flora are found in the hairier flat or disturbed sites on the islands. Species that are known to occur in barrier flat habi¬ tats of all four islands include: Commelina erecta (Commelinaceae), Eleocharis montevidensis, Rhynchospora colorata, Schoenoplectus pungens (Cyperaceae), Sisyrinchium biforme (Iridaceae), Andropogon glomeratus, Eragrostis secundiflora, Paspalum monostachyum , P. setaceum , Schizachyrium scoparium, Spartina patens , S. spartinae, Sporobolus virginicus , Uniola paniculata (Poaceae), Blutaparon vermiculare (Amaranthaceae), Hydrocotyl bonariensis (Apiaceae), Asclepias oenotheroides (Asclepidaceae), Ambrosia psilostachya, Aphanostephus shirrobasis, Borrichia frutescens, Conoclinium betonicifolium, Erigeron procumbens, Flaveria brownii, Gaillardia pulchella. Heterotheca subaxillaris, Machaeranthera phyllocephala, Palafoxia texana, Ratibida peduncularis (Asteraceae), Polypremum procumbens (Buddlejaceae), Opuntia engelmannii (Cactaceae), Euphorbia bombensis (Euphorbiaceae), Acacia minuata, Chamaecrista fasiculata, Dalea emarginata, Indigofera miniata. Mimosa strigiilosa, Prosopis glandulosa, Rhynchosia americana, Sesbania exaltata (Fabaceae), Sabatia arenicola (Gentianaceae), Linum alatum (Linaceae), Oenothera drummondii (Onagraceae), Samolus ebracteatus (Primulaceae), Bacopa monnieri, Stemodia lanata (Scrophularuiaceae), Physalis cinerascens {Solan¬ aceae), and Phyla nodiflora (Verbenaceae). Common species known to occur in disturbed habitats of barrier islands include: Cyperus retrorsus (Cyperaceae), Cooperia drummondii (Liliaceae), Bothriochloa lagnraides, Cenchrus spinifex, Chloris cucuUaia, Cynodon dactylon,, Eragrostis secundiflora (Poaceae), Tidestrornia lanuginosa (Amaranthaceae), Hydrocotyle bonariensis (Apiaceae), Asclepias oenotheroides (Asclepidaceae), Ambrosiapsilostachya, Aphanostephus skirrobasis, Erigeron procumbens, Gail- lardia pulchella, Heterotheca subaxillaris, Iva texensis, Palafoxia texana, Ratibida peduncularis, Sonchus Nelson et al.— Comparison of Flora of Barrier Islands, Texas 21 oleraceus, Verbesina encelioides (Asteraceae), Heliotropium curassavicum (Boraginaceae), Cakile lanceolata, Lepidium virginicum (Brassicaceae), Polypremum procumbens (Buddlejaeeae), A triplex pentandra (Chenopodiaceae), Croton capitatus (Euphorbiaceae), Acacia minuata, Dalea emarginata, Indigofer a miniata, Me li lotus indicus, Mimosa strigillosa, Pediomelum rhombifolium, Prosopis glandulosa, Rhynchosia americana, Sesbania exaltata (Fabaceae), Boerhavia coccinea (Nyctaginaceae), Oenothera drummondii, O. laciniata, O. speciosa (Onagraceae), Argemone albiflora (Papaveraceae), Portulaca pilosa (Portolacaceae), Richardia bras i liens is (Rubiaceae), Lycium carolinianum, Physa- lis cinerascens (Solanaceae), Phyla nodiflora. Verbena halei (Verbenaceae), and Cissus incisa (Vitaceae) (Table 1). Many species that comprise the flora of southern Padre Island are weedy and grow in waste places (Lonard et al,, 1978). This is true for many of the species included in the common flora of the barrier islands. Endangered and threatened species Three species that occur on the barrier islands are listed by the Texas Organization for Endangered Species (TOES). Sesuvium trianthemoides (Aizoaceae) is designated TOES, category III (Jones et al, 1997). This designation indicates S. trianthemoides is in dan¬ ger of becoming extinct in Texas and lacks legal pro¬ tection. Helianthus praecox (Asteraceae) and Cucurbita texana are desgnated TOES, category V (Jones et al., 1997), This designation indicates these two species lack legal protection and are on a watch list for plants with low population numbers or restricted ranges. In the Coastal Bend region of Texas, S . trianthemoides is rare (personal communiction with B. Carr of the Na¬ ture Conservancy). It is possibly only known from the barrier flat of Padre Island National Seashore (Negrete et al., 1999). Helianthus praecox ssp. runyonii is frequent on coastal sands (Jones, 1982) and occurs on Padre Island National Seashore (Negrete et al., 1999). Cucurbita texana occurs along rivers and bays on the mainland (Correll and Johnston, 1979; Jones, 1982) but is also known from Matagorda Island (MeAlister and McAlister, 1993). Concluding remarks In this investigation, we compare the flora of northern Padre Island to that of Matagorda Island, Mustang Island and southern Padre Island, Texas. Families with the greatest representation on all four islands are the Asteraceae, Fabaceae, and Poaceae. These three families constitute greater than 40% of the species found on the barrier islands. Thirty-two families, 78 genera, and 84 species are common to all four islands. Only one species occurring as a part of the common flora is endemic, none are endangered or threatened, most are native herbs, and about 40% are grasses or marsh-dwelling plants. The richest flora is on northern Padre Island with 456 species followed by Matagorda Island (299), south¬ ern Padre Island (216), and Mustang Island (183). In all cases, the island floras are not as rich as the main¬ land floras but share affinities with the nearest main¬ land. Northern Padre Island has the greatest number of genera and species limited to the island. Of these limited taxa, northern Padre Island has the most wet¬ land species, Matagorda Island has the most woody species, and all four islands have many limited species associated with sandy soils, occurring in small popu¬ lations, and ruderal. Flaveria brownii and Sporobolus tharpii are en¬ demic to Texas and Tamaulipas barrier islands. Thirty- one species are endemic to Texas and found on the barrier islands included in this investigation. Three species are especially rare and of interest to conserva¬ tion managers. Sesuvium trianthemoides is listed by TOES as in danger of extinction. Helianthus praecox ssp. runyonii and Cucurbita texana lack legal protec¬ tion and are on a watch list for plants with low popu¬ lation numbers or restricted ranges. Coefficients of community indicate that the flora of northern Padre Island is most similar to that of Matagorda Island and these differences may be caused by climatic changes that occur as one moves from north to south along the Texas coast. In addition, anthropogenic and natural disturbances likely influence extinction rates on the smaller islands resulting in higher than normal Z values for species richness and ende¬ mism as compared to island area. 22 Occasional Papers. Museum of Texas Tech University Acknowledgments The authors thank Paul Eubank and Darrell Echols at PINS, R. Nelson and M. Goetze and students at TSU for field assistance. In addition, unpublished re¬ search reports on file at PINS provided invaluable in¬ formation. Of these, we especially acknowledge re¬ ports by J. T. Baccus, J. K. Horton, and P. D, Carangelo, F. B. Jones, as well as C. A. Rechethin and H. Passey. The authors appreciated support from Organized Fac¬ ulty Research at TSU. Literature Cited Amos, B. 1991. Phytogeographical investigation of Texas endemics. Unpublished list of target species. Anonymous. 1998. Terrain Navigator, ed. 1.0. Maptech, Greenland, New Hampshire. Britton, J. C. and B. Morton. 1989. Shore ecology of the Gulf of Mexico. University of Texas Press. Aus¬ tin. Brower, J., J. Zar, and C. von Ende. 1990. Field and laboratory methods for general ecology , third edition. William C. Brown Publishers, Dubque, Iowa. Carr, W. and D. Diamond. 1995. No place but Texas: Plant taxa endemic to the lone star state. Texas Natural Heritage Program. Unpublished list of endemic taxa. Cornell, D. S. and M. C. Johnston. 1970. Manual of the vascular plants of Texas, Texas Research Foun¬ dation, Renner, Texas. Duncan, W. H. and M. B. Duncan. 1987. The Smithsonian guide to seaside plants of the Gulf and Atlantic Coasts. Smithsonian Institution Press. Wash¬ ington, D, C. Gillespie, T. S. 1976. The flowering plants of Mustang Island, Texas—An annotated checklist. Texas Journal of Science 27: 131-148. Gould, F. W. and T. W. Box. 1965. Grasses of the Texas Coastal Bend. Texas A&M University Press, College Station, Texas. Hatch, S. L., J. L. Schuster, and D. L. Drawe. 1999. Grasses of the Texas Gulf Prairies and Marshes. Texas A&M University Press, College Station, Texas. Jones, F. B, 1982. Flora of the Texas Coastal Bend , 3rd ed. Welder Wildlife Foundation, Sinton, Texas. Jones, S. D,, J. K. Wipff, and P. M. Montgomery. 1997. Vascular Plants of Texas, A comprehensive checklist including synonymy, bibliography, and index. University of Texas Press, Austin. Judd, F. W., R. I. Lonard, and S. L. Sides. 1977. The vegetation of South Padre Island, Texas, in rela¬ tion to topography. Southwestern Naturalist 22: 31-48. Lonard, R. 1. and F. W. Judd. 1980. Phytogeography of South Padre Island, Texas. Southwestern Natu¬ ralist 25: 313-322. Lonard R. I., F. W. Judd, and S. L. Sides. 1978. Annotated checklist of the flowering plants of South Padre Island, Texas. Southwestern Naturalist 23: 497- 510. MacArthur, R. H., and E, O. Wilson. 1967, The theory of island biogeography . Princeton University Press, Princeton, New Jersey. McAlister, W.H. and M.K. McAlister. 1993. A naturalist’s guide: Matagorda Island. University of Texas Press, Austin. Negrete I. G., A. D. Nelson, J. Goetze, L. Macke, T. Wilburn, and A. Day. 1999. A Checklist for the vascular plants of Padre Island National Seashore. Si da 18: 1241-1259. Nelson, A. D., J. R. Goetze, l. G. Negrete, V, E. French, M. P. Johnson, and L. Macke. 2000. Vegetational analysis and floristics of four communities in the Big Ball Hill region of Padre Island National Sea¬ shore. SouthwestemNaturalist45: 431-442. Richardson, A. 1995, Plants of the Rio Grande Delta. University of Texas Press, Austin. Weise, B. and W. A. White. 1980. Padre Island National Seashore: A Guide to the Geology t Natural Environments, and History of a Texas Barrier Island. Un i ver si ty of Tex as, A ustin. Nelson et al.— Comparison of Flora of Barrier Islands, Texas A ddresses of au th o rs: Adam Lucksinger Allan Nelson Department of Biological Sciences Tarleton State University Box T-0100 Stephenville, Texas 76402 e-mail: nelson@tarleton.edu Department of Biological Sciences Tarleton State University Box T-0100 Stephenville, Texas 76402 e-mail: nelson@tarleton. edu Jim Goetze Science Department Laredo Community College Laredo, Texas 78040 e-mail: jrgzoo@lmfonIine.com Publications of the Museum of Texas Tech University It was through the efforts of Horn Professor J Knox Jones, as director of Academic Publications, that Texas Tech University initiated several publications series including the Occasional Papers of the Museum. This and future editions in the senes are a memorial to his dedication to excellence in academic publications. Professor Jones enjoyed editing scientific publications and served the scientific community as an editor for the Journal of Mammalogy, Evolution, The Texas Journal of Science, Occasional Papers of the Museum, and Special Publications of the Museum. It is with special fondness that we remember Dr. J Knox Jones. Institutional subscriptions are available through the Museum of Texas Tech University, attn: NSRL Publications Secretary, Box 43191, Lubbock, TX 79409-3191. Individuals may also purchase separate num¬ bers of the Occasional Papers directly from the Museum of Texas Tech University. ISSN G149-175X Museum of Texas Tech University\ Lubbock, TX 79409-3191