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Nesom, G.L 2010. Infrageneric classification of l/e/ftdy7a(Verbenaceae). Phytoneuron 2010-11: 1-15. Mailed 13 May 2010. 

Guy L. Nesom 

2925 Hartwood Drive 

Fort Worth, TX 76109, USA 


The genus Verbena sensu stricto in the present account includes 70 species (6 currently in the 
process of description). The genus is divided into three sections: 1. Sect. VERBENA, type V. 
officinalis (including 10 series: ser. Verbena; ser. Haleae Nesom, ser. now, type V. halei; ser. 
Plicatae Nesom, ser. nov, type V plicata; ser. Simplices Nesom, ser. nov, type V simplex; ser. 
Connaticarpae Nesom, ser. nov., type: V carnea; ser. Leptostachyae Schauer, lectoiype (designated 
here) V. urticifolia; ser. Candelabrae Nesom, ser. nov., type V striata; ser. Bracteatae Nesom, ser. 
nov., type V bracteata; ser. Californicae Nesom, ser. nov., type V californica; and ser. Tricesimae 
Nesom, ser. nov., type V. canescens); 2. Sect. AifPHEPEIROS Nesom, sect, nov., type V. glabrata 
(including 2 series: ser. Austrobrasilienses Nesom, ser. nov., type V hirta; and ser. Pacificae 
Nesom. ser. nov., type V glabrata); and 3. Sect. VERBENACA Walpers, lectotype (designated here) V 
bonariensis (including 2 series: ser. Pachystachyae Schauer, type V. bonariensis; and ser. Litorales 
Nesom, ser. nov., type V. litoralis). The three sections are delimited primarily on the basis of 
inflorescence structure. 
KEY WORDS: Verbena, Verbenaeeae, infrageneric classification, sections, series 

The only inclusive, critical study of North American Verbena L. sensu stricto has been 
provided by Perry (1933). Moldenke's contributions "toward a monograph of the genus" (1961- 
1964) covered all of the taxa. but they were oriented toward nomenclature and literature and did not 
provide evaluation of patterns of variation; nor did Moidenke provide a key to species, except in a 
few regional floristic accounts. Since a recent overview by Sanders (2001), most of the native South 
.American taxa have been examined in revisionary detail (O'Leary et al. 2007; Nesom 2010a); certain 
groups of the North American species have been studied in detail (Nesom 2010b, 2010c, 2010f, 
2010g). O'Leary et al. (2010) present a revision of the species they consider to represent lineages 
apart from the primary ones of South America — included are species native to the USA Mexico, 
South America, and Europe. The Flora of North America treatment (Nesom submitted) includes the 
native and naturalized species of North America north of Mexico. 

Verbena in the account here includes 70 species. Other recent estimates (e.g. Sanders 2001, "40 
to 50" species; O'Leary et al. 2007 and 2010, 45 and 44 species, respectively) have been generally 
similar, but Atkins (2004) estimated between 200 and 250 species, even though she treated both 
Glandularia Gmelin and Junellia Moidenke as segregates of Verbena. The species of Verbena series 
Pachystachyae Schauer (sensu O'Leary et al. 2007) are native to South America; five of these are 
naturalized elsewhere in the work! Most of the remaining species are North American and Central 
American, except for two European species, V. supina L. and V. officinalis L., which apparently are 
most closely related to North American natives. Australian segregates of V officinalis have been 
recognized (Michael 1997; Munir 2002; comments in Nesom 20 10b), Two species of northwestern 
South America also are hypothesized here to be closely related to V officinalis. 

Tribe Verbeneae Schauer includes Verbena, Glandularia (ca. 100 species), Junellia (ca. 30 
species, including the monoUpic Urbania Phil.), and Mulguraea O'Leary & Peralta (19 species) 
(O'Leary et al. 2009). Hierobotana Briq. (1 species, H. inflata (Kunth) Briq.) also has been included 
among these (e.g., Atkins 2004), but its status apparently remains unresolved — its disposition was not 
mentioned in O'Leary et al. (2009), even under the subheading "Relationship among genera of Tribe 
Verbeneae; Verbena, Glandularia, Junellia and Mulguraea.'''' This group is characterized by fruits 
that separate into four 1-seeded mericarps, mostly parallel anther thecae often with dilated and 
glandular connective, and 2-lobed styles with the anterior lobe stigmatic. Glandularia has its center 
of diversity in South America and Junellia and Mulguraea occur only in that area. The largest 
number of Verbena species occurs in Mexico and the USA Botta (1989) included Tamonea Aublet 
(6 species) as part of this group, but Atkins (2004) and O'Leary et al. (2008) have placed it in tribe 
Casselieae. Verbena carnea Medik. has been treated as the monotypic genus Stylodon Raf, based 
primarily on its mericarps that are connate at maturity, but in other features, V. carnea is similar to 
North American species of Verbena and the connation of mericarps is interpreted here as a derived 
feature within the genus. Recent DNA studies of the Verbeneae (Marx et al. in prep., Dick Olmstead 
pers. comm.) indicate that both Hierobotana and. Stylodon evolved from within, the evolutionary 
matrix of Verbena sensu stricto. 

Phylogenetic reconstructions by Yuan and Olmstead (2008a, 2008b) indicate that Glandularia 
and Verbena are monophyletic sister groups, together having a sister relationship to Junellia sensu 
stricto (O'Leary et al. 2009). Phylogenetically basal to tribe Verbeneae is the newly described 
Mulguraea, a genus, like Junellia, primarily of the arid Andean region. 

The close it-latiutisbip between Verbena and Glandularia is emphasized by the discovery (Yuan 
& Olmstead 2008a) that two independent intergeneric chloroplast transfers have occurred, both from 
Verbena to Glandularia. "'One is from a diploid North American Verbena species [V. hastata or V. 
orcuttiana, as sampled] to a polyploid North American Glandularia species [G. bipinnatifida (Nutt.) 
Nutt, as sampled]. The other is more ancient, from the South American Verbena group [sect. 
Verbenaca] to the common ancestor of a major Glandularia lineage [including G. canadensis (L.) 
Nutt.], which has radiated subsequently in both South and North America." 

Most, infrageneric classifications of Verbena have included Glandularia and/or Junellia, and 
Verbena species have mostly been grouped in series or unranked groups (Walpers 1845; Schauer 
1847; Briquet 1895; Small 1933; Troncoso 1974). Moldenke (1961) simply repeated the system of 
Walpers. O'Leary et al. (2007) studied only South American species, placing them all in 2 subseries 
within series Pachystachyae Schauer. O'Leary et al. (2010) divided the remaining species (ser. 
Verbena) among three unranked groups; Verbena, Hastatae, and Bracteosae. Sanders (2001) 
arranged the species of the southeastern USA into five informal groups. Among the few (14) species 
of Verbena sensu stricto sampled in a molecular phylogenetic studies by Yuan and Olmstead (2008a, 
2008b) and Yuan et al. (2010), essentially two main species groups are evident, corresponding 
essentially to South American and North American species. Cladistic positions of the few-sampled 
North American species are inconsistent among data sets and types of analyses. 

In their classification of Verbena, O'Leary et al. (2007, 2010) have divided the species between 
two groups, emphasizing two basic types of stem anatomy: Type A — cortical parenchyma continuous 
and discrete along the circumference, not interrupted at the stem angles by columns of sclerenchyma 
(their Fig. 2C); and Type B — cortical parenchyma interrupted at the stem angles by thick columns of 
sclerenchyma joined to the angular tissue (their Fig. 2D). Type B anatomy is characterized externally 
by a sharply 4-angled appearance and more prominent development of the angular nerves. All of the 
species except V. rigida of their "subser. Pachystachyae" (= ser. Pachystachyae in the present 
arrangement) are characterized by Type B anatomy. All of these are South American. O'Leary et al. 

placed. South American species with Type A anatomy (excq^t for V. rigida) within subseries 
Pseudoracemosae, a morphologically heterogeneous group dispersed here among ser. 

Austrobrasilienses and ser. Verbena. Native North American species have Type A anatomy, fide 
O'Learyetal. (2010). 

In preparation of a taxonomic treatment of" Verbena for the Flora of North America North of 
Mexico. I have attempted to delimit natural groups within the genus. 

The three sections are recognized within Verbena, primarily based on inflorescence structure. 

1. Infloreseen^. paniculate, *\itli spiles ^ohtan ox irregularly arranged, not in definite 3's; spikes not 
subtended by prominent foliaceous bracts, all spikes pedunculate; stem anatomy Type A 

1. Inflorescence cymose, with spikes in definite 3's; spikes subtended or not by foliaceous bracts, 
middle spike sessile or subsessile to pedunculate; stem anatomy Type A or B. 

2. Spikes not subtended by foliaceous bracts; stems usually sharply 4-angled or (in ser. Litorales) 
some not; leaves indistinctly petiolate through attenuate leaf bases; stem anatomy mostly Type B 

sect. Verbenaca 

2. Each spike subtended by foliaceous bracts; stems not sharply 4-angled; leaves distinctly petiolate 
from truncate to cuneate leaf bases; stem anatomy Type A sect. Amphepeiros 

A character of fruit morphology appears to be predictive, as inferred from its consistent 
correlation with others in the distinction of natural groups. In some species, the developing fruit is 

essentially flat at the apex, and the style base is inserted at that level, at the juncture of the four 
nutlets. When the nutlets separate at maturity, the commissural faces appear to extend to the very tip 
of the nutlets. In other species, the style base is inserted in a depression in the middle of the nutlets, 
and when the nutlets separate at maturity, the dorsal side (the outer) of the nutlets is higher than the 
ventral side (the inner, with the commissural face), giving the appearance that the commissural face 
does not reach the nutlet apex. 

Basis of the study 

Thirty-two species occur in the FNANM flora area, and I also have studied representatives of 
almost all of the rest of the species. The present report summarizes observations based on study of 
the entire collections of Verbena sensu stricto (all geographic areas) from the following institutions: 
ARIZ (800 collections). BRIT-SMU (ca. 1000), MO (ca. 1800), NLU (ca. 800), and TEX-LL (ca. 
1200, the Moldenke Verbenaceae collection). The ability to study additional type specimens through 
online images from F, GH, NY, US, and others has been especially useful. In addition to ^hs FNA 
treatment (32 species, submitted), documentation is provided for various taxonomic decisions in a 
series of collateral papers (Nesom 2010a, 2010b, 2010c, 2010d, 2010e, 2010f, 2010g). 

The native geographic range of each species is broadly characterized below as USA, Mexico, 
Central America, or South America. If a species occurs in more than one of these areas, the area of 
widest distribution is listed first. 

VERBENA L., Sp. PI. 1: 18. 1753; Gen. PI. ed. 5, 12. 1754. LECTOTYPE (Jarvis etal., List Linn. Gen. 

Names Types, 98, 1993): Verbena officinalis L, 

1. Section Verbena 

Stems not sharply 4-angled; leaves broad to narrow, petiolate or basally attenuate, lobed or 

unlobed, margins serrate; inflorescence paniculate, with spikes usually not in definite 3's; spikes not 
subtended by foliaceous bracts, all spikes usually pedunculate; fruits remote to densely overlapping at 
maturity. Stem anatomy Type A 

la. Series VERBENA 

Verbena [unranked] Schizophyllae Walpers, Repert. Bot. Syst. 4: 23. 1845. LECTOYPE (designated 

here): Verbena officinalis L. 
Verbena [unranked] Officinales Small, Man. S.E. Fl. 1135. 1933. TYPE: Verbena officinalis L. 

Plants taprooted or fibrous-rooted; stems erect at the base, sometimes apparently strongly 4- 
angled (perhaps similar to those of sect. Verbenacal); leaves petiolate to subpetiolate, lobed to 
unlobed, blades thin, veins not impressed adaxially, margins serrate with acute teeth, not revolute; 
spikes solitary to few, with a tendency to occur in pairs, especially at the proximal 1-2 nodes of the 
inflorescence, fruits remote or becoming remote proximally; floral bracts usually shorter than the 
calyx or equal; rachis glandular oi eglandulai ^.ommj^uijl faces reaching the nutlet tip. 

Verbena officinalis L. Europe; 2n = 14, 28, 42, 56 
Verbena supina L. Europe; 2n = 14 

Verbena gaudichaudii (Briquet) P.W. Michael Australia 
Verbena macrostachya F. Mueller Australia 
Verbena sororia D. Don Australia/Africa 

Verbena grisea Rob. & Greenm. South Anerica (Galapagos Islands) 

Verbena demissa Moldenke South America (Ecuador) 

Verbena caniuensis Moldenke South America (s Brazil) 

Verbena filicauits Schauer South Anerica (Brazil, Sao Paulo) 

Verbena gradSeseens (Chamisso) Herter South Anerica (Argentina, Bolivia, Paraguay. Uruguay): 

Verbena swiftiana Moldenke South America (Argentina, Misiones; Brazil, Rio Grande do Sul) 
Verbena townsendii Svenson South America (Ecuador, Galapagos Islands) 

The widely dispersed nativity of ser. Verbena, as constituted here, is unusual compared to other 
groups of the genus, which are geographically more coherent, and suggests that the geographical 
subsets need to be examined for the possibility of greater evolutionary independence. Significant 
differences between V. officinalis and V. supina suggest that even they are not most closely related to 
each other. The South American species placed here also constitute a heterogeneous group, 
morphologically and geographically. 

Munir (2002) treated a group of morphologically and geographically distinct Australian 
population systems at varietal rank within Verbena officinalis. Michael (1997) recognized three of 
these taxa at specific rank (as above), distinct from naturalized V. officinalis, and the other two 
probably should treated similarly (see comments in Nesom 20 10b). One of these Australian entities is 
naturalized in Africa (or vice versa); another may be naturalized in Mexico (Chiapas) and Guatemala, 
or else the latter plants represent an undescribed species (Nesom 2010b). Reported variability in 
ploidy level (diploid, tetraploid, hexaploid, octopioid) gives plausibility to the view that 

differentiation within V. officinalis sensu lato may include discrete evolutionary entities appropriately 
recognized by formal nomenclature. 

O'Leary et al. (2010) have indicated that Verbena sororia D. Don and V. officinalis var. 
natalensis Hochst. ex C. Krauss are the correct names at specific and varietal rank for the taxon 
treated in recent literature as Verbena africana (R. Fernandes & Verdcourt) P.W. Michael and V. 
officinalis var. africana (R. Fernandes & Verdcourt) Munir. O'Leary et al, treat it at varietal rank but 
have included other segregates, including the Australian taxa, as synonyms of typical V. officinalis. 

Verbena grisea, an endemic of the Galapagos Islands, is distinct in its small, highly dissected 
La\L ~\„nk drstnKued along the <tem 'terr^ ind lea 1 e-* mJ s f rprhte~ dinanl u ant' graMsh with 
densely hispid-hirsute vestiture, spikes elongate and very slender, and tiny flowers and fruits (corolla 
limb ca. 2 mm in diam., calyces 1.8-2 nun long, nutlets 1-1.2 mm long) slightly overlapping in fruit 
and relatively compactly arranged. The spikes mostly in pairs are like those of ser. Verbena, as are 
the nutlet commissural faces reaching the very tip. Its placement here is provisional but provides a 
basis for a hypothesis regarding its occurrence in the Galapagos, especially since it would be 
anomalous within any of the South American groups. In addition to images of the holotype and 
isotype (GH!), I have examined the following: Galapagos Islands: Duncan Island, rare around 1250 ft, 
15 Aug 1905-06, Stewart 3316 (CAS photo-LL!); Pinzon [Isla Pinzon = Duncan Island], near summit, 
1200 ft, rare, fls light blue, to 70 cm, Sep 1975, van cler Werfj'2322 (LL!). 

Verbena demissa is endemic to Andean Ecuador (known from provinces Azuay, Canar, and 
Pichincha). It is distinctive in morphology: stems numerous, prostrate and sometimes apparently 
rooting at the nodes, radiating from a thick, woody taproot; stems and rachises sparsely strigillose and 
sparsely stipitate-glandular; leaves small (6-20 mm), short-petiolate, obovate or elliptic-obovate to 
oblanceolate, the margins serrate with 2-3(-5) pairs of coarse teeth or shallow lobes; spikes relatively 
short (1-7 cm) and few -flowered, mostly solitary, less commonly with paired proximal spikes, the 
fruits becoming remote and somewhat divergent; flowers small (limbs ca. 2 mm in diam.); and fruits 
1.6-1.8 mm, with commissural faces reaching the nutlet tips. Verbena demissa is similar to other 
species of the group in features of habit, stem anatomy (fide O'Leary et al. 2010) and morphology, 
glandular vestiture, the mostly solitary, short and few-flowered spikes, and nutlet morphology. 

Verbena caniuensis is distinctive in its creeping habit and inflorescence reduced to a single 
spike, habital features shared with the geographically similar V. filicaulis. O'Leary et al. (2007) 
further discussed the distinctive inflorescence of V. caniuensis. On the other hand, its ovate-orbicular, 
coarsely serrate, narrowly petiolate leaves are unusual in ser. Verbena. 

Verbena filicaulis is unusual among species of South American Verbena in its deeply 3-parted or 
pinnately 5-parted leaves, especially in combination wdth its apparently rhrzomjtous habit solitary 
spikes, and larger flowers and fruits,. O'Leary et al. (2007) allied V. filicaulis with the species placed 
here in sect. Amphepeiros ser. Austrobrasilienses. 

Verbena swiftiana Moldenke is similar to V filicaulis in its deeply 3-lobed (with narrow 
divisions) to coarsely toothed lower' and mid-cauline leaves and short, few-flowered, mostly 
unbranched spikes with remote fruits. The stems are glabrous, mostly unbranched, and often 
procumbent and rooting at the nodes. The type (isotype: NY digital image!) and the few other known 
collections from northeastern Argentina (Misiones), with one collection from immediately adjacent 
Brazil (Rio Grande do Sul). 

Verbena gracilescens is a common and abundant species of central and southeastern South 
America (Argentina, Bolivia, Paraguay, Uruguay). It characteristically produces relatively short 

(mostly 5-15 cm), very slender spikes with remote fruits extending to the base or nearly so 
(essentially without peduncles). The inflorescence is dichotomously branched, but often irregularly 
so. The stems are branching, sometimes decumbent and nodally rooting, and glabrous or very 
sparsely strigillose along the angles. Flowers are very small (calyces 1.2-1.5 mm), and the leaves are 
sharply serrate and often tripartite, especially the basal to mid-cauline. 

In their characteristic morphology, Verbena swiftiana and V. gracilescens are conspicuously- 
different, but O'Leary et al. (2010) have treated them as conspecific varieties, apparently emphasizing 
several cited specimens (without locality data) that are said to represent "una gradacion continua" 
between the two. I have not seen the putative intergrades, but interspecific hybrids are not unsual in 
Verbena and such have not been interpreted in other instances as evidence of conspecificity. O'Leary 
et al., however, did not include Misiones, Argentina, or any of Brazil in the range of V. gracilescens. 
thus its geographic range, apparently allopatric w r ith that of V. swiftiana, would preclude 
hybridization. The putative intergrades cited possibly may be populational variants within V. 

Moldenke (1968, 1971) recognized Verbena townsendii, V. galapagosensis Moldenke, V. 
stewartii Moldenke, and V. glabrata var. tenuispicata Moldenke as native taxa of the Galapagos 
Islands. From study in herbarium and field, Van del' Werff (1977) concluded that they all belong to 
one single, extremely variable species (by far the most variable in the whole genus, in my 
observations of collections at MO and TEX-LL), the oldest name being V. townsendii. According to 
Van der Werff, differences in leaf width and lobing apparently result from habitat differences, 
position on the stem, and maturation of the plants— juvenile leaves usually are broader. Forms of V. 
townsendii are very similar to V. gracilescens. 

lb. Series SlMPLICES Nesom, ser,. nov. Type: Verbena simplex Lehm. 

Foliis sessilibus angustis nonlobatis, spicis 1 vel paucis fructibus dense superpositis, vestimento 
eglanduloso, et nuculis superficiebus commissuralis apices attengentibus distinctus. 

Plants taprooted; leaves linear to narrowly lanceolate or narrowly oblong-oblanceolate, sessile, 
unlobed, margins few-toothed, not revolute, blades thick with veins not impressed adaxially; spikes 
mostly 1 or few from proximal branches, fruits remaining dense and overlapping; floral bracts shorter 
than the calyces; rachis eglandular; commissural faces appaix *! w\ten In * c npLtJ' to the nutlet 

Verbena simplex Lehman USA; 2n = 14 

Verbena simplex has no apparent close relatives, at least in eastern North America. It is similar 
to V carnea in its tendency to produce sessile, unlobed leaves and fruits with commissural faces 
extending completely to the nutlet tips. 

O'Leary et al. (in press) have treated Verbena orcuttiana as conspecific with V simplex. The 
two differ in growth habit, vestiture, leaf arrangement, and floral features; they are very different in 
ecology and their native geographic ranges at their closest point are disjunct by more than 1100 miles. 
Verbena orcuttiana lias many similarities with V. californica and V. abramsii, and those three species 
are treated here as ser, Californicae. Given the apparently isolated position of V. simplex in the 
eastern USA it would be reasonable, at least as a hypothesis, to consider the possibility that it is 
closely related to ser. Californicae. 

le. Series CONNATICARPAE Nesom, ser. nov. TYPE: Verbena cornea Medikus 

Duratione perenni habitu rhizomato, foiiis sessilibus, spicis plerumque solitariis, floribus relative 
amplis distinctus, et nuculis connatis non discedentibus ad maturitatem. 

Plants rhizomatous; leaves sessile, oblong-spatulate, unlobed, margins closely serrate to 
irregularly crenate-serrate, revolute, blades thick with veins impressed adaxially; spikes mostly 1 or 
few, slender, fruits becoming remote; floral bracts usually shorter than the calyx or equal; rachis 
eglandular; nutlets connate, not separating at maturity, commissural faces apparently extending 
completely to the nutlet tips. 

Verbena carnea Medikus USA 

Sanders (2001) hypothesized that Verbena carnea is close to V. stricta (here placed in ser. 
Candelabrae), but the rhizomatous habit and the thickened, unlobed leaves with closely serrate 
margins are without a close match elsewhere in the genus. The reduced inflorescence and the connate 
nutlets are specialized features, suggesting that V. carnea is derived from some North American 
group. There is a tendency in a number of North American species for the nutlets to remain adherent 
until very late in ontogeny, and the developmental persistence of this feature in V. carnea is hardly a 
character that would justify segregation at generic rank. 

O'Leary et al. (2010) have adopted Verbena caroliniana Michx. (1803) as the correct name for 
this species, as preferred over the earlier V. carnea Medikus (1784). Comments and a neotype 
justifying retention of the Medikus name are provided by Nesom (20 lOd). 

Id. Series L.EPTOSTACHYAE Schauer in DC, Prodr. 11: 545. 1847. LECTOTYPE (designated here): 

Verbena urticifolia L. Troncoso (1974, p. 311) designated Verbena officinalis as the lectotype of 
series Leptostachyae, but V officinalis is automatically the type of series Verbena. 

Plants taprooted or fibrous-rooted; leaves petiolate, unlobed, margins serrate with acute teeth, 
blades thin with veins not impressed adaxially; spikes numerous, often strictly in 3 's at lower nodes, 
slender, fruits distantly remote; floral bracts usually shorter than the calyx or equal. laJu* egl.mdulai , 
commissural faces extending to very tip of nutlets. 

Verbena Carolina L. Mexico, sw USA, Central America; In = 14 
Verbena ehrenbergiana Schauer Mexico; 2n = 14 
Verbena scabra Vahl USA. West Indies, Mexico 
Verbena urticifolia L. USA 2n = 14 

The plants of ser. Leptostachyae are easily recognizable by their eglandular vestiture, numerous, 
long, very slender spikes with remote fruits, tiny corollas, and nutlets with commissural faces 
^ .kiulinv l<- vu l . Iip^'^v .^ _'"!"■. i 

le. Series CANDELABRAE Nesom, ser. nov. TYPE: Verbena stricta Ventenat 

Verbena [unranked] Hastatae Small, Man. S.E. Fl. 1135. 1933. TYPE: Verbena hastata L. 

Foiiis latis grosse serrato et spicis numerosis crassiusculis fructibus dense superpositis distinctus. 

Plants taprooted or fibrous-rooted; leaves distinctly petiolate to subsessile, unlobed, margins 

usually coarsely serrate to incised with acute teeth, blades thickened with veins impressed adaxially; 
spikes numerous and clustered from distal nodes, thick, fruits densely overlapping; floral bracts 
usually shorter than the calyx or equal; rachis eglandular; commissural faces extending to very tip of 

Verbena hastata L. USA; 2n = 14 
Verbena macdougalii Heller USA, Mexico; In = 14 
Verbena stricta Ventenat USA; 2n = 14 
Verbena xutha Lehman USA; 2n = 42 

Verbena stricta and V. macdougalii are very similar between themselves and probably related as 
sister species. Verbena hastata stands apart in its reduced vestiture and relatively long-petiolate 
leaves with serrate margins; a close relationship with ser. Leptostachyae should be investigated. 
Verbena xutha is provisionally placed here, emphasizing its eglandular vestiture, spikes arising from 
distal branches and often remaining relatively compact, and nutlets with commissural faces extending 
to very tip of nutlets. The laeiniate leaves of V. xutha, however, are more similar to some of those of 
ser. Plicatae. The polyploid chromosome number of V. xutha at least allows the possibility that it 
incorporates more than one genome. 

If. Series BRACTEATAE Nesom, ser. nov. TYPE: Verbena bracteata Lag. & Rodr. 
Verbena [unranked] Bracteosae Small, Man. S.E. Fl. 1135. 1933. TYPE: Verbena bracteata Lag. & 
Rodr. (incl. Verbena bracteosa Michx.) 
Foliis latis serrato-incisis, spicis densis bracteis longi-protrusis, et fruetibus ad maturitatem plus 
minusve remotis distinctus. 

Plants taprooted or fibrous-rooted; leaves petiolate to subsessile, often 3-lobed, margins serrate 
to deeply incised with acute teeth, blades relatively thin, veins not impressed adaxially; spikes few, 
thick, fruits densely overlapping but sometimes becoming somewhat remote at maturity; floral bracts 
becoming much longer than the calyx and coiolla. uchis -glandulai, eommi'-smal faces extending to 
very tip of nutlets. 

Verbena bracteata Lagasca & Rodr. USA, Mexico; 2n = 14, 28 

Speuilizjhun^ of Verbena bracteata \±\ habit (prostrate) and inflorescence (mostly solitary, 
elongate spikes with greatly enlarged bracts and relatively large fruits) give the species a distinctive 
appearance. The petiolate, incised leaves, eglandular vestiture, and nutlets with commissural faces 
extending completely to the tip are similar to those of V. xutha. 

lg. Series HALEAE Nesom, ser. nov. TYPE: Verbena halei Small 

Foliis crassibus venis adaxialiter impressis marginibus revolutis caulium lobatis et spicis 
numerosibus fruetibus late remotis ad maturitatem distinctus. 

Plants taprooted; leaves petiolate to subpetiolate, basal lobed to unlobed, cauline lobed, margins 
serrate with acute teeth, blades thick veins impressed adaxially; spikes numerous, slender, fruits 
becoming remote; floral bracts usually shorter than the calyx or equal; rachis eglandular; 
commissural faces ending below the nutlet tips. 

Verbena halei Small USA, Mexico; 2n = 14 

Verbena halei has been treated as element of V. officinalis, as V. halei subsp. halei (Small) S. 
Barber, but the two rarely if ever have the opportunity even to hybridize, much less to intergrade. 
The consistent morphological differences and continental disjunction in native range support the 
I of V. halei at specific rank. 

An individual of Verbena menthifolia from Arizona studied by Yuan and Olmstead (2008b) 
was heterozygous at both the PHOT1 and PHOT2 nuclear gene loci, and the gene trees indicated that 

the individual was of hybrid origin, with V. halei as one of the putative parental species. 

lh. Series PLICATAE Nesom, ser. nov. TYPE: Verbena plicata Greene 

Foliis latis plerumque 3-lobatis segmentis inciso-dentatis venis saepe abaxialiter prope margines 
albidis el spicis 1 velpaueis di-tinctus 

Plants taprooted; leaves usually petiolate, relatively broad (oblong-ovate or obtusely elliptic- 
ovate), cauline sometimes subclasping, often 3-parted, margins coarsely serrate to incised-serrate or 
pinnately lobed-serrate, blades thick, veins impressed adaxially, often whitish abaxially near the 
margins; spikes 1 or few, dense with overlapping fruits to elongate and slender with fruits becoming 
remote; floral bracts usually shortei ilru< the .. t ih\ >! equal uJii usujiH "hndu^ai ~omjrussUial 
faces ending below the nutlet tips (except in V. xutha). 

Verbena cloverae Moldenke USA; In = 14 

Verbena plicata Greene USA Mexico; 2n = 14 

Verbena runyonii Moldenke USA 2n = 14 

Verbena lasiostachys Link (incl. V. robusta Greene, V. prostrata W.T. Ait.) exico; 2n = 14 

Among these species, Verbena plicata and V. cloverae share a distinctive feature of the nutlets — 
the commissural faces are bullate with low plates densely packed and perhaps connate, forming 
essentially an unbroken white surface. The Californian V. lasiostachys appears to belong in ser. 
Plicatae but is distinct in geography compared to the others, which are mostly in the south-central 
USA. O'Leary et al. (2010) treated V. runyonii as a synonym of V. neomexicana var. hirtella Perry. 

li. Series CALIFORNICAE Nesom, ser. nov. TYPE: Verbena californica Moldenke 

Foliis plerumque oblanceolatis dentatis, fructibus dense imbricatis vel remotis, rhachidibus 
calycibusque glandulosis, etnuculis superficiebus commissuralis apices attengentibus distinctus. 

Plants taprooted; leaves elongate, not lobed, without distinct petioles, margins toothed, revolute, 
surfaces not glossy, veins impressed adaxially; spikes 1 or 2-5 from medial to distal branches, 
relatively thin, fruits not overlapping or densely overlapping but becoming remote proximally; floral 
bracts shorter than the calyx or equal; rachises and calyces glandular; commissural faces extending 
completely to the nutlet tips 

Verbena abramsii Moldenke USA 
Verbena californica Moldenke USA 
Verbena orcuttiana Pern' Mexico 

These three species are very similar in aspect to those of ser. Tricesimae. Their recognition here 
as a separate group emphasizes the distinctive nutlet morphology and their Californian geography 
(Nesom 2010 f, in manuscript). 

Ij. Series TRICESIMAE Nesom, ser. nov. TYPE: Verbena canescens Kunth 

Folu 3 eionoatts nmnatiiidus \el pciiiu* daitahs, lamiius incrassatis venis adaxaiiter impressis 
marginibus revolutis, spicis 1 vel paucis relative tenuibus fructibus plerumque proxime remotis 

Plants taprooted; leaves elongate, pinnatifid to deeply toothed (incised-pinnatifid or incised 
dentate, varying to subentire), blades thickened., veins impressed adaxially, margins revolute, surfaces 
glossy; spikes 1 or few, relatively thin, fruits becoming remote proximally; floral bracts shorter than 
the calyx or equal; rachises glandular or eglandular; commissural faces not reaeliing the nutlet apex. 

Verbena canescens Kunth Mexico, USA; 2n = 14 

Verbena gracilis Desfontaines Mexico, USA 

Verbena hirteila (Perry) Nesom, ined. Mexico, USA; 2n = : 14 

Verbena jessicae Nesom & Hinton, ined. Mexico 

Verbena johnstonii (Moldenke) Nesom Mexico 

Verbena livermorensis Turner & Nesom, ined. USA, Mexico 

Verbena moranii Nesom, ined. Mexico 

Verbena neomexicana Small Mexico, USA; In = 14 

Verbena nitens Nesom, ined. Mexico 

Verbena perennis Wooton USA; 2n = 14 

Verbena pinetorum Moldenke Mexico, USA 

Verbena subuligera Greene Mexico 

Verbena xylopoda (Perry) Nesom ined. USA, Mexico 

The sectional epithet alludes to the 30th parallel, which most of the species are near. Verbena 
canescens and V. gracilis have wide ranges compared to the others, from the southwestern USA to 
south-central Mexico. Verbena abramsii, V californica and V. orcuttiana, at the northwestern corner 
of this group, stand apart from the other species in their elongate, serrate leaves and commissural 
faces of the nutlets extending completely to the nutlet tips — these perhaps represent a distinct group. 
The species of ser. Trices imae are treated in detail in Nesom (2010g, in manuscript) and Nesom and 
Hinton (2010, in manuscript; V. jessicae), where the species noted above as "ined." will be formally 
described or delimited. 

Sanders (2001) hypothesized that Verbena neomexicana is part of the species group that includes 
V. menthifolia, and indeed they have similarities in. habit. Verbena menthifolia, however, and its 
putatively close relative V. madrensis have thinner leaves with non-revolute margins and veins not 
impressed adaxially, and the commissural faces generally extend completely to the nutlet tips. 

2. SECTION AMPHEPEIROS Nesom, sect. nov. TYPE: Verbena glabrata Kunth 

Inflorescentiis cymosis spicis in. 3s, quoque spica per folia vel bracteas foliaceas subtenta, 
et foliis latis distincte petiolatis e basi truncatis vel cuneatis marginibus grosse serratis distinctus. 

Stems not sharply 4-angled (Type A anatomy); leaves broad, distinctly petiolate from truncate to 
euneate leaf bases, unlobed, margins coarsely serrate; inflorescence cymose, with spikes in definite 
3's; each spike subtended by foliaceous bracts, often with the middle spike sessile or subsessile to 

short-pedunculate; fruits usually densely overlapping at maturity. 

2a. Series PACIFICAE Nesom, ser. nov. TYPE: Verbena glabrata Kunth 

Distributione geographica plerumque secus oceanum pacificum distinctus. 

Verbena glabrata Kunth South America (Bolivia, Ecuador, Columbia, Peru) 

Verbena macrodonta Perry Mexico (Raja California Sur) 

Verbena recta Kunth Mexico 

Verbena sedisla Moldenke South America (Galapagos Islands) 

Species of ser. Pacificae are autochthonous to both the South American and North American 
(also see ser. Pachystachyae regarding V. sphaerocarpa; ser. Verbena is the only group 
hypothesized here to be more widepread). The separation of ser. Brasilienses and ser. Pacificae, 
based on geography, hypothesizes that other distinctions remain to be discovered; a clear 
morphological difference is not apparent, but the geographically-based names provide reference to the 
groups. Tt also is acknowledged that the separation may be arbitrary. 

Verbena macrodonta is one of a number of endemic species of the oak and pine-oak woodlands 
of the Sierra de la Laguna of Baja California Sur. Pine-oak forests closest to those of the Sierra de la 
Laguna are in the trans -volcanic ranges of southeast and south-central Mexico, the "Serranias 
Meridionales" floristic province, tide Rzedowski (1978). Pine-oak forests of northern Baja California 
(Sierra Juarez, Sierra San Pedro Martir) are more closely related floristically to the USA. 

1 have seen only the holotype (MO!) and isotype (US digital image!) of Verbena macrodonta, 
but the distinctive leaf morphology and inflorescence structure, as well as its geography, justify its 
placement among these species. The leaves are large, broadly lanceolate to oblong-lanceolate with 
coarsely serrate margins and truncate or rounded bases and distinct petioles, and the spikes are dense, 
subtended by bracts, and distinctly in 3's. Verbena macrodonta and V. recta both, are unusual in sect. 
Amphepeiros because of their pedunculate spikes. O'Leary et al. (2010) have placed V macrodonta 
as a synonym of V. officinalis. 

Verbena glabrata is native to western South America. O'Leary et al. (2007) identified and cited 
far-disjunct collections from Mexico (Michoacan, Puebla, and Veracruz) as V. glabrata, but these 
Mexican plants are V. recta. O'Leary et al. (2010) have recognized V. recta as distinct but without 
clarifying their earlier equation of it with V. glabrata. I have seen collections of V. recta from the 
Mexican states of Distrito Federal, Edo. Mexico, Michoacan, Morelos, Nuevo Leon, Oaxaca, and 
Puebla. The populations in Nuevo Leon appear to be disjunct from the others but morphologically 

Collections identified as Verbena glabrata from the southernmost portion of its range (Depto. 
Arequipa in Peru) are of prominently glandular plants with trilobed and more elongate leaves than 

characteristic elsewhere. It is probable that these represent an undescribed species. 

2b. Series AUSTRO BRASILIENSES Nesom, ser. nov. TYPE: Verbena hirta Sprengel 
Distibutione geographica plerumque in Brasilia auslrali distinctus. 

Verbena hirta Sprengel South America (s Brazil, ne Argentina) 

(tentatively including var. hirta and var. gracilis Dusen) 
Verbena lobata Velloso South America (s Brazil) 

(tentatively including var. lobata and var. glabrata Moldenke) 
Verbena subpetiolata N. O'Leary 7 South America (s Brazil) 

All three species of ser. Austrobrasilienses are centered in southernmost states of Brazil, Parana, 
and Rio Grande do Sul, hence the series epithet. This is a morphologically heterogeneous assemblage 
needing further study. 

3. SECTION Verbenaca Walpers, Repert. Bot. Syst. 4: 14. 1845. LECTOTYPE (designated here): 

Verbena bonariensis L. Sect. Verbenaca of Walpers included Verbena, Glandularia, and 
Junellia. The lectotype is chosen here to represent to restrict the section to Verbena sensu stricto. 
Schauer (1847) followed Walpers in his broad concept of sect. Verbenaca, placing V officinalis 
within sect. Verbenaca series Lepiosiachyae. 

Stems usuall} sharply 4-angled (Type B anatomy); leaves broad to narrow, indistinctly petioiate 
thiouglt aienuaL Lii biSw unlobui irsiiin.n^ w srsely serrate to subentire; inflorescence cymose, 
with spikes in definite 3's; spikes not subtended by fbiiaceous bracts, often with the middle spike 
sessile or subsessile to pedunculate; fruite densely overlapping or becoming remote at maturity. 

3a. Series PACHYSTACHYAE Schauer in DC, Prodr. 11: 539. 1847. LECTOTYPE (Troncoso 1974, p. 

311): Verbena bonariensis L. O'Leary et al. (2007, p. 580) cited "serie Pachystachyae subserie 

Pachystachyae Schauer," perhaps supposing that the subseries was automatically established. 

"Subseries Pachystachyae" is not a legitimate name. 
Verbena [unrankedj Foliosae Walpers, Repert. Bot. Syst. 4: 18. 1845. LECTOYPE (designated here): 

Verbena bonariensis L. 
Verbena [unranked] Micranthae Walpers, Repert. Bot. Syst. 4: 18. 1845. LECTOYPE (designated 

here): Verbena bonariensis L. 
Verbena [unranked] Holophyllae Walpers, Repert. Bot. Syst. 4: 18. 1845. LECTOYPE (designated 

here): Verbena bonariensis L. 
Verbena [unranked] Bonarienses Small, Man. S.E. Fl, 1135. 1933. TYPE: Verbena bonariensis L. 
Verbena [unranked] Venosae Small, Man. S.E, Fl. 1 135. 1933 TYPE: Verbena rigida Spreng. 

Fruiting spikes relatively short and thick, the central sessile to subsessile, with fruits usually 
densely overlapping at maturity. Leaves unlobed. 

Verbena alata Otto ex Sweet South America 

Verbena bangiana Moldenke South America 

Verbena bonariensis L. South America; 'In = 14, 28 

Verbena brasiliensis Velloso (incl. V intercedens Briquet) South America 

Verbena ephedroides Chamisso South America 

Verbena goyazensis Moldenke South America 

Verbena hispida Ruiz & Pavon South America; 2n = 14 

Verbena incompta P.W. Michael South America 

Verbena intermedia Gillies & Hooker ex Hooker South America; 2n = 28, 35, 56 

Verbena lindbergii Moldenke South America 

Verbena ovata Chamisso South America; In =- 72 

Verbena rigida Sprengei South America; 'In = 42 

Verbena sagittalis Chamisso South America 

Verbena sphaerocarpa Perry Mexico (Socorro Island) 

Verbena valerianoides Kunth South America 

Verbena rigida was observed by O'Leary et al. (2007) to have Type B stem morphology, unlike 
the rest of the section. It also is unusual in it rhizomatous habit, but in features of the inflorescence it 
is similar to the species placed here in ser. Verbenacae. 

Verbena sphaerocarpa is tentatively recognized at specific rank (Nesom 2010a). It is endemic 
to Socorro Island (about 600 kilometers west of the coast of Colima, Mexico) but is very similar to V. 
brasiliensis and probably derived from it. 

Verbena valerianoides is a distinctive species apparently endemic to montane Colombia (the 
type from Bogota, P fiche!) It produces sessile, non-clasping, narrowly lanceolate to oblong- 
lanceolate, entire leaAes and short thiJ i r> ss the cen'i s] cne ^hL O'Leary et al. (2007) 
considered this a "doubtful taxon" but I have seen recent collections from the departments of Boyaca, 
Cundinamarca, and Narino. 

Verbena bangiana was treated by O'Leary et al. (2007) as V. hispida var. obovata (Moldenke) 
O'Leary, who noted that they 7 did not consider differences in vestiture and floral dimensions between 
the two taxa as "sufficiently important in Verbena'' to sq?arate them as distinct species. Collections 
of each are numerous and intermediates appear to be rare, suggesting that the two are reproductively 

Verbena goyazensis (Bull. Torrey Bot. Club 77: 404. 1950. TYPE: Brazil. Goias. Rio do Peixe, 
8 Jul 1949, G. Hashimoto 663 [holotype: SP, fragment-NY digital image!]) has broad, sessile, serrate 
leaves and very short, congested spikes in 3's — it appears to be remarkably distinct in its leaves with 
deeply reticulate-excavate abaxial surfaces. It has been included by O'Leary et al. (2010) as a 
"doubtful taxon." 

3b. Series LlTORALES Nesom, ser. nov. TYPE: Verbena litoralis Kunth 

Spicis fructiferis relative elongatis gracilibusque fructibus proximalibus remotis ad maturitatem 
etfoliis nonlobatis distinctus. 

Fruiting spikes elongate and slender, the central pedunculate, with fruits becoming remote at 
maturity, at least proximally; leaves unlobed. 

Verbena litoralis Kunth South America (western); 2n = 28, 42, 56 
Verbena montevidensis Sprengel South America (southeastern); 2n = 21, 42 

Both of these species, as currently identified, appear to be polymorphic. Potential correlations 
between ploidy level and morphology apparently have not been investigated. 


This study was done in conjunction with preparation of the FNA treatment of Verbena and 
supported by the Flora of North America Association. I am grateful to Nataly O'Leary for providing 
a pre-print copy of the 20 10 Verbena revision authored by her and associates Mulgura and Morrone 
and to Dick Olmstead for providing a copy of a submitted manuscript, multi-authored, with first 
author Hannah Marx. 


Atkins, S. 2004. Verbenaceae. In K. Kubitzki (ed.), The Families and Genera of Vascular Plants. 

Vol. 7: 449-468. 
Botta, S.M. 1989. Studies in the South American genus Junellia (Verbenaceae, Verbenoideae) I. 

Delimitation and infrageneric divisions. Darwiniana (San Isidro) 29: 371-396. 
Briquet, J. 1895. Verbenaceae. In A. Engler & K. Prantl (eds.), Naturalichen Pflanzenfamilien IV, 

3a. 1915, Nachtr. 3,4: 132-182. 
Martinez, S., S. Botta, y M.E. Mulgura. 1996. Morfologia de las inflorescencias en Verbenaceae- 

Verbenoideae. I: Tribu Verbeneae. Darwiniana 34: 1-17. 
Michael, P.W. 1997. Notes on Verbena officinalis s.s. and V. macrostachya (Verbenaceae) with new 

combinations in two closely related taxa. Telopea 7: 293-297. 
Moldenke, H.N. 1961-1965. Materials toward a monograph of the genus Verbena. I. Phytologia 8: 

95-104. 1961. II. Phytologia 8: 108-152. 1962a. III. Phytologia 8: 175-216. 1962b. IV. 

Phytologia 8: 230-272. 1962c. V. Phytologia 8: 274-323. 1962d. VI. Phytologia 8: 371-384. 

1962e. VII. Phytologia 8: 395-453. 1962f. VIII. Phytologia 8: 460^196. 1963a. IX. 

Phytologia 9: 8-54. 1963b. X. Phytologia 9: 59-97. 1963c. XI. Phytologia 9: 113-181. 

1963d. XII. Phytologia 9: 189-238. 1963e. XIII. Phytologia 9: 267-336. 1964a. XIV. 

Phytologia 9: 351^107. 1964b. XV. Phytologia 9: 459-480. 1964c. XVI. Phytologia 9: 501- 

505. 1964d XVII. Phytologia 10: 56-88. 1964e. XVIII. Phytologia 10: 89-161. 1964f. XIX. 

Phytologia 10: 173-236. 1964g. XX. Phytologia 10: 271-319. 1964h. XXI. Phytologia 10: 

406^116. 1964i. XXII. Phytologia 10: 490-504. 1964J. XXIII. Phytologia 11: 1-68. 1964k. 

XXIV. Phytologia 11: 80-141. 19641. XXV. Phytologia 11: 155-213. 1964m. XXVI. 

Phytologia 11: 219-287. 1965a. XXVII. Phytologia 11: 290-357. 1965b. XXVIII. Phytologia 

11:400-422. 1965c. XXIX. Phytologia 11:435-507. 1965A 
Moldenke, H.N. 1968. The vervains collected on the Galapagos Islands by Charles Darwin during 

the voyage of the "Beagle." Phytologia 16: 340-342. 
Moldenke, H.N. 1971. Verbena. Pp. 503-509, in I.L. Wiggins and D.L. Porter. Flora of the 

Galapagos Islands. Stanford University Press, Stanford California. 
Munir, A.A. 2002. A taxonomic revision of the genus Verbena L. (Verbenaceae) in Australia. J. 

Adelaide Bot. Gard 20: 21-103. 
Nesom, G.L. 20 10a. Taxonomic notes on Verbena bonariensis ( Verbenaceae) and related species in 

the USA. Phytoneuron 2010-12: 1-16. 
Nesom, G.L. 2010b. A new species of Verbena (Verbenaceae) from northeastern Mexico and an 

overview of the V. officinalis group. Phytoneuron 2010-13: 1-14. 
Nesom, G.L. 2010c. Taxonomy of Verbena urticifolia (Verbenaceae) and its close relatives. 

Phytoneuron 2010-14: 1-12. 
Nesom, G.L. 2010d Neotypification of Verbena carnea Medikus (Verbenaceae). Phytoneuron 

2010-15: 1-3. 
Nesom, G.L. 2010e. Typification of Verbena spuria L. (Verbenaceae). Phytoneuron 2010-16: 1-3. 
Nesom. G.L. 20101". Taxonomy of the Verbena californica group (Verbenaceae). Phytoneuron, to 

be published. 
Nesom, G.L. 2010g. Taxonomic overview of the Verbena neomexicana group (Verbenaceae), 

including new species. J. Bot. Res. Inst. Texas, in manuscript, to be submitted. 
Nesom, G.L. and G.S. Hinton. 2010. Verbena jess icae (Verbenaceae), a new species from Nuevo 

Leon, Mexico. Phytologia, in manuscript, to be submitted. 
O'Leary, N., M.E. Mulgura, amd O. Morrone. 2007. Revision taxonomica de las especies del genero 

Verbena (Verbenaceae): serie Pachystachyae. Ann. Missouri Bot. Gard. 94: 571-621. 
O'Leary, N., P. Peralta, and M.E. Mulgura. 2008. A taxonomic revision of the genus Tamonea 

(Verbenaceae). Bot. J. Linn. Soc. 157: 357-371. 
O'Leary, N., Y.-W. Yuan, A. Chemisquy, and R.G. Olmstead. 2009. Reassignment of species of 

paraphyletic Junellia s.l. to the new genus Mulguraea (Verbenaceae) and new circumscription 

of genus Junellia: Molecular and morphological congruence. Syst. Bot. 34: 777-786. 
O'Leary, N., M.E. Mulgura, & O. Morrone. 2010. Revision taxonomic de las especies del genero 

Verbena (Verbenaceae). II. Serie Verbena. Am. Missouri Bot. Garden, in press. 
Perry, L.M. 1933. A revision of the North American species of Verbena. Ann. Missouri Bot. Gard. 

20: 239-363. 
Rzedowski, J. 1978. Vegetacion de Mexico. Editorial Limusa, Mexico, D.F. 
Sanders, RW. 2001. The genera of Verbenaceae in the southeastern United Stales. Harvard Pap. 

Bot. 5: 303-358. 
Schauer, J.C. 1847. Verbenaceae. In AP. De Candolle (ed.), Prodr. 11: 522-700. 
Small, J.K. 1933. Manual of the Southeastern Flora. Univ. of North Carolina Press, Chapel Hill. 
Troncoso, N.S. 1974. Los generos de Verbenaceas de Sudamerica extratropical (Argentina. Chile, 

Bolivia, Paraguay, Uruguay, y Sur de Brazil), Darwiniana (San Isidro) 18: 295-412. 
van der Werff, H. 1977. Vascular plants from the Galapagos Islands: New records and taxonomic 

notes. Bot. Not. 130: 89-100. 
Walpers, W.G. 1845. Verbenaceae. Repert. Bot. Syst. 4: 3-134. Addendum in 6: 686-693. 1847. 
Yuan, Y-W. and R.G. Olmstead. 2008a. A species-level phylogenetic study of the Verbena complex 

(Verbenaceae) indicates two independent intergeneric chloroplast transfers. Molec. Phylog. 

Evol. 48: 23-33. 

Yuan, Y-W. and R.G. Olmstead. 2008b. Evolution and phylogenetic utility of the PHOT gene 

duplicates in the Verbena complex (Verbenaceae): Dramatic intron size variation and footprint 

of ancestral recombination. Amer. J. Bot. 95: 1166-1176. 
Yuan, Y.-W., C. Liu, H.E. Marx, and R.G. Olmstead. 2010. An empirical demonstration of using 

pentatricopeptide repeat (PPR) genes as plant phylogenetic tools: Phytogeny of Verbenaceae 

and the Verbena complex. Molec, Phylogen. Evol. 54: 23-35.