BIOLOGY MAR 1 9 'C79 The person charging this material is re- sponsible for its return to the library from which it was withdrawn on or before the Latest Date stamped below. Theft, mutilation, and underlining of books are reasons for disciplinary action and may result in dismissal from the University. To renew call Telephone Center, 333-840O UNIVERSITY OF ILLINOIS LIBRARY AT URBANA-CHAMPAIGN L161— O-1096 FIELDIANA: BOTANY A Continuation of the BOTANICAL SERIES o/ FIELD MUSEUM OF NATURAL HISTORY VOLUME 31 FIELD MUSEUM OF NATURAL HISTORY CHICAGO, U. S. A. 520.5 •FB vi 31 TABLE OF CONTENTS PAGE 1. Two New Species of Palms from Nicaragua. By S. F. Classman ... 1 2. Tropical American Plants, VI. By Louis 0. Williams 11 3. Agriculture, Tehuacan Valley. By C. Earle Smith, Jr 49 4. Flora, Tehuacan Valley. By C. Earle Smith, Jr 101 5. Preliminary Studies in the Palm Genus Syagrus Mart, and Its Allies. By S. F. Glassman 145 6. Tropical American Plants, VII. By Louis 0. Williams 165 7. Supplement to Orchids of Guatemala. By Donovan S. Correll .... 175 8. Preliminary Notes on Scrophulariaceae of Peru. By Gabriel Edwin . . 223 9. New Species in the Palm Genus Syagrus Mart. By S. F. Glassman . . 233 10. Tropical American Plants, VIII. By Louis 0. Williams 247 11. Notes on the Flora of Costa Rica, I. By William C. Burger 273 12. A New Eurystyles from Nicaragua. By Alfonso H. Heller 279 13. New Species in the Palm Genus Syagrus Mart. By S. F. Glassman . . 285 14. A Revision of the Family Geastraceae. By Patricio Ponce de Leon . . 303 15. Studies in American Plants. By Dorothy N. Gibson 353 16. Two New Nicaraguan Juglandaceae. By Antonio Molino R 357 17. Studies in the Palm Genus Syagrus Mart. By S. F. Glassman .... 363 18. Tropical American Plants, IX. By Louis O. Williams 401 If FLORA, TEHUACAN VALLEY - EARLE SMITH- JR- w FIELDIANA: BOTANY VOLUME 31, NUMBER 4 Published by CHICAGO NATURAL HISTORY MUSEUM FEBRUARY 26, 1965 FLORA, TEHUACAN VALLEY C. EARLE SMITH, JR. Associate Curator, Vascular Plants FIELDIANA: BOTANY VOLUME 31, NUMBER 4 Published by CHICAGO NATURAL HISTORY MUSEUM FEBRUARY 26, 1965 Library of Congress Catalog Card Number: 65-1 8866 PRINTED IN THE UNITED STATES OF AMERICA BY CHICAGO NATURAL HISTORY MUSEUM PRESS CONTENTS PAGE LIST OF ILLUSTRATIONS 105 GEOGRAPHY AND TOPOGRAPHY 107 CLIMATE 107 DESCRIPTION OF THE VEGETATION 109 Montane rainforest 109 Oak-pine forest 112 Thorn-scrub cactus vegetation 116 Lime-soil facies 123 Saline-soil facies 129 RELATIONSHIPS OF THE TEHUACAN FLORA 133 SUMMARY 141 REFERENCES . I43 LIST OF ILLUSTRATIONS PAGE 26. Tehuacan valley seen from the village of Apala in the region of oak-pine forest 108 27. Beneath the tree canopies of the rainforest, the soil surface is never closely covered with herbaceous species 110 28. In drier areas the trees are scattered and the shrub vegetation forms a nearly continuous cover Ill 29. Beneath the canopy of oak-pine forest, the rough bark of the oak trees is frequently covered by epiphytic lichens 113 30. A tree on the edge of an arroya near Coxcatlan 115 31. The vegetational cover for most of the Tehuacan valley is thorn-scrub and cacti 117 32. One of the largest columnar cacti is Lemaireocereus weberi 118 33. The trunk of Fouquieria formosa HBK. is covered with greenish-yellow bark which peels in sheets 120 34. The tallest tree of the area is pochote 122 35. A limestone formation from which the vegetation was cleared for culti- vation 124 36. Another variation in the vegetation of the Tehuacan valley is conditioned by the outcropping of lime rock 125 37. Among the most interesting cacti of the lime soil area is Ferrocactus robustus 126 38. Colonies of Mammillaria collina Purpus are frequent among the shrubs . 127 39. The cactus Echinocactus grandis Rose 128 40. Stretches of open saline soil visible from top of Petlanco 130 41. The Rio Salado river 131 42. A thunderhead over the Tehuacan valley mountains 132 43. Random rain clouds over the top of the Sierra de Zongolica 132 TABLES PAGE 1. Family and Geographic relationships of 253 species of Tehuacan area plants .... . 142 Flora, Tehuacan Valley GEOGRAPHY AND TOPOGRAPHY The Tehuacan valley lies about 150 km. southeast of Mexico, D.F., in the southeastern corner of Puebla. It extends into the northern edge of Oaxaca. The Mexico-Veracruz highway follows the gentle slope of the valley from Tlacotepec in the northwest to Puerto del Aire at the top of the Sierra Madre Oriental on the north- east. The valley is about 170 km. long by 40 km. wide. It is bounded on the northeast by the ridges of the Sierra Madre Oriental, or Sierra de Zongolica, which separate the states of Vera Cruz and Puebla. To the southwest, the valley is rimmed by the lower masses of the Sierra de Zapotitlan. The northernmost areas of the valley are higher in elevation, the land falling away in a series of giant steps to the south. The area is drained by the Rio Salado and Rio Grande, which join to form part of the Papaloapan drainage. The collections on which this paper is based were made while I was co-operating in a study of botanical fragments recovered in con- nection with archeological investigation of caves in the valley area. The plant collections reported here will serve as vouchers against which the recovered material will be identified. The archeological and the botanical work are being carried out under the auspices of the Proyecto Arqueologico-Botanico "Tehuacan" of the R. S. Pea- body Foundation with grant funds made available by the National Science Foundation and the Rockefeller Foundation. Richard S. MacNeish of the National Museum of Canada, Human History Branch, is Director of the Tehuacan project. CLIMATE The climate of the Tehuacan valley is largely controlled by the mass of the Sierra de Zongolica rising to the northeast between the valley and the Gulf of Mexico. The valley floor, lying at about 1500 m. elevation at Tehuacan, drops off to about 650 m. elevation at Tecomovaca, Oaxaca, but the mountains along the side of the 107 108 FIELDIANA: BOTANY, VOLUME 31 valley rise to elevations in excess of 3000 m. The mountains effec- tively remove much of the moisture from the trade winds blowing in from the sea. The average annual rainfall in the Tehuacan area is 478 mm. (see fig. 43) ; monthly averages range from 2 mm. in Jan- uary to 119 mm. in September with the greatest portion of the pre- cipitation occurring from June to September (Contreras, 1942). This climate is classed as dry. FIG. 26. Tehuacan valley seen from the village of Apala in the region of oak- pine forest, where it is relatively level with a few low hills. Beyond can be seen the rugged masses of the Sierra de Zapotitlan along the western side of the valley. At the opposite end of the valley at Cuicatlan, Oaxaca, the rain- fall is less. Cuicatlan has an annual average rainfall of only 301 mm., with the heaviest precipitation in June and the lightest in January and February, when the rainfall is so slight that it is normally not measurable. Here the climate is classed as very dry. No other rec- ords are available for the Tehuacan valley, but it is evident that the precipitation pattern over the valley is far from uniform. Many local areas receive considerably less rainfall than the annual average SMITH: FLORA, TEHUACAN VALLEY 109 recorded at Tehuacan. This contrasts markedly with stations in Vera Cruz, like Orizaba, which reports an annual average rainfall of 2116 mm. DESCRIPTION OF THE VEGETATION The vegetation of the valley below the 1800 m. level can best be described as thorn-scrub and cactus. Undisturbed vegetation above this elevation is oak-pine forest. Where the ridge is sufficiently high and exposed so that it is almost constantly wet, a true montane rain- forest develops. An excellent description of the vegetation of the Papaloapan drainage area, of which the Tehuacan valley forms a part, is given by Faustino Miranda (1948) and provides an extended background for the hypotheses presented later in this paper. Montane rainforest The vegetation of the montane rainforest at the top of the Sierra de Zongolica is a continuous cover, with crown heights of 15 to 20 m. Seen from above, it looks remarkably smooth with few overtopping trees, unlike the canopy of lowland rainforest. Within the forest, the boles of the trees of the upper story are free of limbs for 6 to 10 m. Except where the forest cover is broken by steep barrancas, the un- derstory is limited to scattered individual trees. As the margin of the forest along the barrancas is approached, an understory of me- dium-sized tree species appears and the forest floor is closely covered with a shrub cover. The vegetation in the barrancas is an almost impassable tangle of large shrubs, small trees and tree ferns. In the high-canopy forest, lianas climb into the tree tops and epiphytic vegetation is plentiful on the upper parts of the boles and along the branches. Collections in the rainforest were limited since rainforest vegeta- tion does not appear among the plant fragments recovered during the archeological operations in the valley. Of the canopy trees, only Prunus barbata Koehne was collected, as there was insufficient time to fell trees or use climbing apparatus. The occasional understory trees include Clethra mexicana DC. with its crown nearly covered with white flowers, Ternstroemia tepezapote S. & C., the most abun- dant small tree, with glossy dark green foliage, and Rapanea jurgensii Mez., with twigs closely covered with purple fruit. In the barrancas, 1 See also: Smith, Agriculture in the Tehuacan Valley, Fieldiana: Botany, Vol. 31, No. 3. 110 FIELDIANA: BOTANY, VOLUME 31 FIG. 27. Beneath the canopy, the soil surface is never closely covered with herbaceous species but the open canopy allows copious development of straggling shrubs, many of which are spiny. two kinds of tree ferns, Alsophila bicrenata (Liebman) Fourn. and A. schiediana Presl, which may grow to be 3 m. tall, spread their light green umbrellas of feathery fronds. The long fronds of Hypolepis repens (L.) Presl appeared from the top to be tree ferns, but they develop no trunk and the fronds rise directly from a horizontal rhi- zome at the surface of the soil. In the barranca, Bouvardia macilenta Blake, which is capped with light yellow flowers, grows to 2 m. in height. Occasionally, Centropogon grandidentatus (Schlecht.) Zahlbr. straggles among the other shrubs, where its few orange flowers are conspicuous. Two other conspicuous straggling plants among the shrubs were Cestrum fasciculatum (Schlecht.) Miers, whose large, FIG. 28. In drier areas the trees are scattered and the shrub vegetation forms a nearly continuous cover. In the foreground is lechuguilla (Agave karwinskii Zucc.) from which a fiber is obtained. To the right can be seen the leaves of Ipomoea walcottiana Rose. Ill 112 FIELDIANA: BOTANY, VOLUME 31 light red flowers are strangely different from those of the commonly cultivated Oestrums, and Phytolacca rugosa Br. & Bouche, which straggles lazily to a length of 5 m. or more. Where the forest is opened along the road, Mikania cordifolia (L. f.) Willd. is festooned with white flowers, and Tibouchina schiediana (L. & C.) Cogn. with its bright magenta flowers provides contrast. In these open borders, Miconia spp. were fruiting heavily. At one place, a stand of Fuchsia microphylla HBK. with its small, bright green leaves and tiny, hang- ing, shining red flowers made a spectacular contrast. Frequently these exposed shrubs are intertwined with vines among which are an Exogonium sp. and Phaseolus coccineus L. with scarlet flowers. Under the high canopy, the stand of shrubby Ardisia liebmannii Oerst. persists only near the margin. Occasionally scattered plants of Asplenium sessilifolium Desv. grow in the soil and the somber darkness is sometimes startingly broken by the bright red plants of Monotropa coccinea Zucc. Near the margin, Passiflora adenopoda DC. hangs its cream and purple flowers among the shrubs and up into the trees. The only identifiable liana recovered was Smilax aristolochiaefolia Mill. The remainder either broke before their tops pulled out of the canopy or were too firmly fastened to come down. Mixed among the epiphytes on the boles of the trees were Polypo- dium lowei C. Chr., Peperomia deppeana S. & C., Peperomia reflexa (L. f.) A. Dietr., Isochilus linearis (Jacq.) R. Br., with its small, pur- ple flowers and grasslike foliage, and the very rare Odontoglossum ehrenbergii Link, Kl. & Otto, with its pink or white flowers splashed with chocolate brown. Oak-pine forest The oak-pine forest at the lower elevations on the western slopes of the Sierra (down to about 1800 m.) is far different in appearance from the rainforest above. Near the upper edge where some of the species of the rainforest intermingle with those of the oak-pine forest, the rainfall is still sufficiently high to maintain a heavy epiphyte population. The canopy is more broken and the increased light allows a much greater development of shrubbery through which one must push. Farther down in the zone of less rainfall, the under canopy of medium-sized trees is entirely eliminated, while the shrub growth is more of an annoyance. Here the forest may be nearly pure stands of either oak or pine or mixtures in any proportion. Local variation appears to be closely linked to subsurface drainage, as little difference in the soil is evident. When a closed cover of FIG. 29. Beneath the canopy of oak-pine forest, the rough bark of the oak trees is frequently covered by epiphytic lichens, but the leaf litter, herbaceous plants and scattered shrubs are reminiscent of temperate North American hard- wood forests. Where the soil is less well drained, as in this forest, oak trees pre- dominate; pine is mixed with oak in better drained areas and becomes a dominant in nearly pure stands on well-drained slopes and knolls. 113 114 FIELDIANA: BOTANY, VOLUME 31 oak is found, the forest looks like temperate zone forests in little- disturbed moist valley areas of New York or Pennsylvania. The rough bark of the trees supports a fine epiphytic population in the canopy, however. The ground cover is of low shrubs of the family Ericaceae or herbs of many genera familiar in temperate zone woods. When the pine is predominant, the canopy is more open and the ground cover is thicker, with a lower percentage of Ericaceae, but grasses and sedges are more marked among the herbaceous plants. Here the maximum height of the canopy probably seldom exceeds 20 m. and heights of 12 to 18 m. are more common. Canopy trees in this forest are much easier to collect. Around and above Apala near Coxcatlan, the most common oaks are Quercus brachystachya Benth. and Q. obtusata H. & B. The pines include Pinus hartwegii Lindl. and P. pseudostrobus Lindl. var. apulcensis Mart. In some places, the ericaceous tree Arbutus xalapensis HBK. is conspicuous, with smooth, cinnamon-colored bark and clusters of orange to red fruit. In openings and around the forest margin, ericaceous shrubs are common. Among the shrubs in the openings are Vaccinium confer- tum HBK., with shining black fruit, Pernettya mexicana Camp and Arctostaphylos conzattii Fern. On the forest floor, Gaultheria parvi- folia Small and Arctostaphylos pungens HBK. occur where the canopy is relatively open. Sometimes Geranium schiedianium Schlecht., bearing magenta flowers, is conspicuous. Erigeron karwinskyanus DC. is one of the most common composites in the area, forming shrubs up to 0.75 m. tall. Around the edges of occasional abandoned milpas Muhlenbergia versicolor Swallen and Stipa ichu (R. & P.) Kunth form a nearly continuous cover broken only occasionally by the deep pink flowers of Oenothera multicaulis R. & P. and the scarlet flowers of Bouvardia ternifolia (Cav.) Schlecht. The forest cover may be nearly solid pine or oak trees depending upon local conditions. Where man or grazing animals have caused little disturbance, the species composition of the associations is prob- ably undisturbed. Thus, in the more open woods with a moist oak litter, Pinguicula sp., with brilliant royal purple flowers, is abundant; where the floor is drier and the litter is lacking, thickets of Lyonia squamulosa M. & G. will occur and the bare soil areas may have local carpets of Sedum muscoideum Rose or Arenaria lycopodioides Willd., the former with yellow flowers and the latter with white. When the oak canopy is heavy and the forest moist, the herbaceous plants may vary from Dahlia scapigera (A. Dietr.) L. & 0. var. australis Sherff, FIG. 30. The stream beds throughout the Tehuacan valley are normally dry, even in the rainy season, but there is ample evidence that occasional storms fill the streams to overflowing. This tree on the edge of an arroya near Coxcatlan began as a seedling on a ground level near the man's right hand. Subsequent flooding deposited nearly five feet of alluvial material around the trunk of the tree and many adventitious roots formed. Still later, another surge of water cut the bank away, again exposing the trunk and base of the tree. 115 116 FIELDIANA: BOTANY, VOLUME 31 Aneilema karwinskyana (R. & S.) Woods., Peperomia campylotropa Hill and Echeveria racemosa Schl., which are tropical in connotation, to Asclepias circinalis (Dene.) Woods., Viola hookeriana HBK., Ox- alis alpina Rose, Didymaea mexicana Hook, f . and Ranunculus petio- laris HBK., all of which lend a temperate forest aspect to the woods. This impression is soon dispelled on looking upward, as the trees are festooned in some areas with vining Struthanthus deppeanus (C. & S.) Blume or the graceful hanging, yellowish-green stems of Phoraden- dron longifolium Eichl., while the limbs are frequently crowded with epiphytic Tillandsia spp., Epidendrum vitellinum Lindl., with bright orange flowers, Echeveria guatemalensis Rose, Peperomia berlandieri Trel. and Polypodium martensii Mett. On the exposed rocky ridges, the oaks may be dwarfed and closely grown together with ericaceous shrubs, all of whose branches are thickly covered with lichens, in- cluding hanging strands of Usnea. Thorn-scrub cactus vegetation Below the oak-pine forest, at about 1800 m. elevation, the change in the vegetational cover is dramatic. Here the rainfall is obviously less, for the forest cover is nearly always open. The maximum height of the canopy is about 6 to 8 m. and is much less in many places. The shape of the trees differs markedly, also. Here the crowns of the trees tend to be umbrella shaped, with contorted branches and many short branchlets. The rough bark of the trees of the montane forest is replaced by the smooth boles or peeling bark usually associated with vegetation in arid areas. The candelabra forms of giant cacti are scattered through the trees and are so abundant locally as to form nearly pure stands of one or two species. Openings are occupied by spreading colonies of prickly pear cacti or the overgrown shrubby mala mujer (Jatropha urens L.). Open stretches of bare soil are re- lieved here and there by colonies of Mammillaria or barrel cacti with only open scattered patches of broad-leaved shrubs. Much of the vegetation bears spines or thorns, or the short shoots are stout and pointed. The leaves on many of the plants are compound and the leaflets small; the simple leaves of many are microphylls. Local variations in the composition of the vegetation seem to de- pend both on edaphic factors and on available moisture. Large areas in the Tehuacan valley are obviously highly alkaline as the base rock is limestone which outcrops on the hillsides and forms a pebble and cobble mixture with the soil. More restricted sites are saline because of local saline springs or because of the continuing use of the partially SMITH: FLORA, TEHUACAN VALLEY 117 FIG. 31. The vegetational cover for most of the Tehuacan valley is thorn- scrub and cacti which most nearly approaches a forest in the vicinity of Coxcatlan. Here many species of trees of the Leguminosae, Burseraceae, Anacardiaceae, and other families are intermixed with columnar cacti. In places, the cacti may form nearly pure stands. The trees are usually short with umbrella-shaped crowns and smooth bark. saline mineral waters of the valley for irrigation. In the major por- tion of the valley area from Tlacotepec in the northwest, to Cha- zumba, Oaxaca, on the west, to Tecomovaca, Oaxaca, in the south, the vegetational cover is uniform although the species composition may vary in percentage. These changes in the vegetational cover seem to relate to local drainage patterns and the amount of water available to the plants. The valley vegetation extends for long distances into the moun- tainsides in the barrancas to the east where it finally meets the moist- area vegetation coming down from the mountains. This extension has been accentuated by the diversion of the normal water drainage in the barrancas into a multiplicity of irrigation channels. Far into the mountains the change to mesophytic vegetation is dramatic even 118 FIELDIANA: BOTANY, VOLUME 31 FIG. 32. One of the largest columnar cacti is Lemaireocereus weberi Britt. & Rose, whose branches grow like the arms of a candelabra. though it is severely restricted by the intensive cultivation of the mountainside above the barranca. In the remnants of what must once have been a more extensive moist forest along the barrancas are found Erythrina americana Mill., with bright red seeds persisting in the open tan pods, Inga paterno Harms, which has an edible white flesh around the seeds, Parathesis aff. chiapensis? nearly solidly covered with creamy-white berries, Ficus cotinifolia HBK., the source of a local bark paper, Solanum verbascifolium L., the leaves of which are used to scour pots, Bocconia arbor ea Wats, and Pterostemon mexicanus Schauer., which was heavily laden with clusters of pink flowers. Shrubs in the open areas include Calliandra capillata Benth. and Anisacanthus gonzalezii Greenm. SMITH: FLORA, TEHUACAN VALLEY 119 with colorful red flowers. The vine Canavalia villosa Benth. twines over the shrubs. In the small patches of forest, Tillandsia spp. are frequent epiphytes and Adenocalymna alboviolaceum Loes. climbs over the tree tops. Herbs are uncommon, but Rivinia humilis L. is conspicuous. In a moist area along the stream Equisetum gigan- teum L. forms a tangled mass. The vegetational cover of the Tehuacan valley has been removed many times and then allowed to recover gradually as the farmers have moved their fields over the gently sloping hills and across the plains. Evidence is good that the population of the valley before historical times may have been considerably larger than at present. Evidences of former large villages and the remains of terraces, check dams and irrigation works, where the vegetational cover now appears to be stable and very old, indicate that even these areas were once cultivated. In spite of the dry climate, recovery of the thorn-scrub cactus vegetation from disturbance must be rapid. It is certainly much faster than is the recovery of mixed hardwood forests in the eastern United States where evidence of disturbance persists for long periods. The markedly uniform composition of the vegetation over the whole area is accentuated by the forms of the individual species. The large cereus-type cacti all lend a similar appearance even though many different species are found in the forests. Trees of the Legumi- nosae, Anacardiaceae and Burseraceae tend to have similar bark and crown shape although the details of the foliage, flowers and fruits readily distinguish them. The masses of shrubs have a sim- ilar straggly, sparsely-foliaged appearance but many different plants are involved. Only when the plants are in full bloom is the tremen- dous variety of the vegetation displayed. Common trees in the valley are Acacia subangulata Rose, Cassia pringlei Rose ("tecuahuile" whose foliage and bright yellow flowers are fed upon by dark striped caterpillars which are called by the same name and are locally considered a delicacy when fried in deep fat), Acacia villosa (Sw.) Willd., Mimosa luisana Brandg., Acacia cymbispina Sprague and Riley, and Acacia sericea M. & S., all of the Leguminosae. Zizyphus pedunculata (Brandg.) Standl., with its green and red marble-like fruits, locally called "cholulo," is used for soap. Actinocheita filicina (DC.) Barkley and Juliana adstringens Schlecht. are similar in appearance but the latter is readily distin- guished by its winged fruit. Celtis pallida Torr. provides a contrast with simple foliage and much branched extremities. Bursera sub- 120 FIELDIANA: BOTANY, VOLUME 31 FIG. 33. The trunk of Fouquieria formosa HBK. is covered with a thin, smooth greenish-yellow bark which peels in sheets. Bark of this texture is common to many trees or the valley. moniliforme Engl. is the largest of all of the burseras. Morkillia mexicana (Moc. & Sesse") Rose & Paint, is particularly evident when bearing its large magenta flowers. Equally distinctive is Thouinid- ium insigne (Brandg.) Standl. with inflated, winged, tan fruit hang- ing in clusters. The occasional specimens of Tecoma stans (L.) HBK. or Thevetia peruviana (Pers.) Merr., with bright yellow flowers, are conspicuous. Hintonia standleyana Bull, is sometimes 8 m. tall and nearly covered with large white flowers. Perhaps the largest tree SMITH: FLORA, TEHUACAN VALLEY 121 of the whole formation is the "pochote," Ceiba parvifolia Rose, whose trunk and limbs are covered with corky, thick spines when it is young. Among the most unusual appearing trees are Jatropha neopauci- flora Pax, with very thick twigs and bursera-like fruit, and Manihot pauci flora Brandg., with Oxalis-\ike foliage, which looks very unlike other species of Manihot. The tree which characterizes the Tehuacan valley forest cover more than any other is Fouquieria formosa HBK., whose peeling, greenish-yellow bark is conspicuous everywhere. Jutting up through the trees of the valley and foothills are indi- viduals and patches of candelabra cacti. One of the most common is "jiotillo," Escontria chiotilla (Weber) Rose, with yellow flowers and laxly branched stems. In contrast are the straight upright stems of Myrtillocactus geometrizans (Mart.) Cons, with tiny, glaucous fruit along the ribs, Lemaireocereus stellatus (Pfeiffer) B. & R. with red flowers, and Lemaireocereus weberi Britt. & Rose with its huge bulk of repeatedly branched arms reaching many meters above the crowns of the surrounding trees. In some places the fuzzy tops of Cephalo- cereus sp. are conspicuous. Few of the shrubby plants grow in compact shapes and some are tortuously intertwined and difficult to collect for botanical speci- mens. Among the more compact are Bursera arida (Rose) Standl. and Jatropha dioica Sesse". Castela tortuosa Liebm. has numerous attrac- tive red fruits. Perhaps the most common and conspicuous strag- gling shrub is Cordia stellata Greenm. with tight balls of white flowers which later mature into bright red fruits, but the morphological com- plexity of the flowers of Ayenia fruticosa Rose, another of the very common shrubs, makes it far more interesting to botanists. Numer- ous shrubby plants with inconspicuous flowers such as Iresine rotund- ifolia Standl., Croton morifolius Willd. var. obtusifolius Mull.-Arg., Cordia brevispicata M. & G., and Croton fragilis var. sericeous Mull.- Arg. intermingle with Echinopterys lappula Juss., Haplophyton cine- reum (A. Rich.) Woods., Perymenium ovatum Brandg., Parthenium tomentosum DC., and Hibiscus brasiliensis L. all of which have rela- tively showy flowers. Included here should be Agave macroacantha Zucc., which forms colonies of glaucous rosettes on the hillsides, Agave rubescens Salm-Dyck., which grows as a sessile rosette, Agave washingtoniensis Baker & Rose? and Agave karwinskii Zucc., a stalked agave locally called "lechuguilla." Thickets of the edible tunas, Opuntia pilifera Weber and Opuntia hyptiacantha Weber, and the scattered "mala mujer," Jatropha urens L., make walking hazardous FIG. 34. The tallest tree of the area is pochote (Ceiba parvifolia Rose) which has distinctive corky spines on the trunk when it is young. The fruit has been collected by the local population since before the Conquest both for the fiber around the seeds and for the seeds themselves which are eaten. 122 SMITH: FLORA, TEHUACAN VALLEY 123 for the unwary. The parasitic shrub, Psittacanthus calyculatus (DC.) Don, with clusters of bright orange flowers, is not uncommon on the branches of various trees. Occasionally Lamourouxia nelsoni Rob. & Greenm. is plentiful and very conspicuous because of its bright red flowers with purple mouths. Over and among the shrubs, Cardio- spermum halicacabum L. frequently throws a webby tangle of stems. The vines Marsdenia zimapanica Hemsl. and Gonolobus fraternus Schlecht. are not uncommon. By far the most common plant in the shrub vegetation is Lantana camara L., whose scattered plants always seem to be in bloom. The herbaceous plant representation is surprisingly varied al- though there is much open ground and the herbaceous vegetation is nowhere very thick. Hechtia sp. sometimes forms extensive colonies on the hillsides. The composite family is represented by Sanvitalia fruticosa Hemsl., Tridax procumbens L. and Pectis canescens HBK. Argemone mexicana L. and Solanum amazonicum Ker. are abundant in disturbed soil along the dry watercourses and the latter is espe- cially abundant along trails and roads. Among the conspicuous weedy herbs is Nicotiana glauca Grah. which may grow as tall as 3 m. In this dry habitat, several fragile looking plants, including Oxalis neaei DC., 0. berlandieri Torr., Talinum paniculatum (Jacq.) Gaertn., Commelina erecta L. and C. dianthefolia Del., are well repre- sented. The smaller cacti which form small cushions with bright red fruit are Mammillaria napina Purpus and M. carnea Zucc. In the dry areas, Selaginella lepidophylla Spring, remains tightly rolled until rainfall provides sufficient moisture for the stems to relax and expose the rich green tops. In the rock crevices of the banks and hillsides, Notholaena Candida Hook, and Cheilanthes microphylla Sw. form clumps. Finally, epiphytic on the trees and candelabra cacti, Tillandsia recurvata L. and another species of Tillandsia are not rare. Whether Opuntia decumbens Salm-Dyck. should be included in the herbs or the shrubs is difficult to decide, since the tuna de viboras is low and succulently herbaceous, but possesses the same stout stem and root structure which characterize upright opuntias. Lime-soil fades The most distinctive vegetation within this general pattern in the Tehuacan valley is the plant association on the areas of shallow soil over limestone. To the north near Azumbilla is a small area of this type, but immediately to the west of Tehuacan at El Riego are nearly cliff -like limestone hills the top of which is known as La Mesa. To 124 FIELDIANA: BOTANY, VOLUME 31 FIG. 35. In the background can be seen the level northern reaches of the Tehuacan valley. The foreground area is the top of a limestone formation from which the vegetation was cleared for cultivation; the fields have been abandoned but remain open. the southwest along the road through Zapotitlan and for intervals as far as the limits of the area at Chazumba, Oaxaca, there are other limestone outcrops both large and small. Among the least disturbed of these is the mesa near the settlement of Teloxtoc. All the limestone areas appear to be so well drained that the tree cover common to the major part of the valley is eliminated. In- stead, a shrubby, conspicuously spiny, vegetational cover is devel- oped. Agaves, cacti, yuccas and hechtias grow in greater abundance. Somehow, flowers on the vegetation seem to be larger and more color- ful. This impression may be false and stem from the low height of the shrubs which allows one to see almost anything blooming. Open areas of soil and rock are prevalent, especially if a pocket heated more intensely by reflection from surrounding rock walls occurs. To the western edge of the area, the only palm seen, Brahea dulcis (HBK.) Mart., grows on lime soil; this palm is the source of fibers used locally to weave hats. Trees in the limestone area are few and frequently scattered in distribution, perhaps due to persistent clearing. Any flat area with SMITH: FLORA, TEHUACAN VALLEY 125 FIG. 36. Another variation in the vegetation of the Tehuacan valley is con- ditioned by the outcropping of lime rock. This limestone mesa top near Teloxtoc is still relatively undisturbed but other areas of this type are under cultivation. The strange Beaucarnea gracilis Lem. trees of the Liliaceae form an open forest interspersed with barrel cacti (Echinocactus grandis Rose) and many species of small shrubs. lime soil usually has been intensively cultivated. The top of La Mesa near Tehuacan is deeply scarred with furrows and the marks of field boundaries are everywhere. Only an occasional Fouquieria formosa HBK. stands above the shrubs. One specimen of Beaucarnea indi- cates that this tree may have once been more plentiful, while occa- sional clumps of Yucca periculosa Baker provide variety across the horizon. In the quebradas cut into the mesa behind El Riego, several tree species occur. Tecoma stans (L.) HBK., with bright yellow flowers, Ptelea trifoliata L., which, when cut, smells like skunk, Mal- pighia galeottiana Juss., a nanche" with pricking hairs and edible fruit, and Hesperothamnus purpusi (Harms) Rydb., with bright magenta flowers, are all small trees seldom exceeding 4 m. in height. The shrubs on the limestone are many and varied. The large cacti, Echinocactus grandis Rose, which grows to 1.5 m. tall and half that in diameter, and Ferrocactus robustus (L. & 0.) B. & R., which 126 FIELDIANA: BOTANY, VOLUME 31 •BBHBHBHi FIG. 37. Among the most interesting cacti of the lime soil area is Ferrocactus robustus (L. & O.) B. & R., which forms large mounds. In the foreground are the gray-green, leafless stems of a plant of Pedilanthus cymbifera Schlecht. forms massive mounds many feet across, are by far the most conspic- uous forms. Nearly as different are the plants of Pedilanthus cymbi- fera Schlecht., with red, slipper-like flowers on gray-green, leafless stems, and "candelillo," Euphorbia antisyphilitica Zucc., the basis of an industry which supplied wax for candles, hence the common name. Hintonia standleyana Bull, is an occasional shrub here. Among the shrubs bearing colorful flowers are Calliandra hirsuta (Don) Benth., with bright red stamens, Salvia thymoides Benth., with bright blue flowers, Zexmenia pringlei Greenm., whose rays and disk are deep yellow, Dalea tuberculina (Rydb.) Herm., with royal purple blossoms, Hibiscus elegans Standl. and Cassia macdougliana Rose, both with yellow flowers, and Berendtiella laevigata (Rob. & Greenm.) Thieret, with reddish-orange, trumpet-like flowers. Less conspicuous shrubs include Croton incanus HBK., C. ciliato-glandu- FIG. 38. Colonies of Mammillaria collina Purpus are frequent among the shrubs. A greater variety of cacti seem to be present on the lime soil areas rather than in other parts of Tehuacan valley. 127 128 FIELDIANA: BOTANY, VOLUME 31 losus Ort. and Lasiocarpus salicifolius Liebm., of the Malpighiaceae but bearing fruit much like Heliocarpus. Herbaceous plants are scattered and never form a very thick cover over the surface of the soil. Part of this sparsity may be due to the inroads of grazing animals which are allowed to feed through all areas of the countryside not actively being cultivated. In sandy 1 .i\V< *' 4- 9 I ^^ • • ^> oo oo • ^^ '^ © • • (M © © • © © O D, © CTi ?D d • • CT> ©