Aliso: a Journal of Systematic and Evolutionary Botany New Euphorbiaceae from Mexico New Euphorbiaceae from Mexico

This article co nta ined descriptions of five new taxa of Me xican Euphorbiaceae. Euphorbia (sub g. Agaloma) na yaren sis is e nde mic to pine-oak woodland in the mount ains of central Nayarit. It appears related to E. so ob yi but differs by possessing linear to linear-ovate leaves. Croton varelae is also endemic to central Nayarit. A key was provided to distinguish this spec ies. a member of sect. Gei-seleria, from the sev en othe r Mex ican species of this section. Cr ot on ram illatus var. magniglandulifer occurs in the states of Guerre ro and Morelos. This new varie ty differs from var. ramillatus by the possession of larger peti olar g lands. Croton michaelii occurs in Agu ascaliente s and Durango. It is uncertain to which sectio n of C rot on this species belongs. It resembl es C ro ton yecorensis but is distinguished by possessing a lepid ote indumentum and by lacking con spicu ou s s tipitate glands. Crot on disjun ctus has been coll ected in Chihuahua and Agua scalientes, at localiti es se parated by more than 600 km. Thi s species appea rs to be most closely akin to Cro ton fru tic ulosus Torr., from which it is se parated by g labrous, ev ident (vs. pube scent, nearl y o bso lete) stipules and multifid (vs. bifid) sty les.


INTRODUCTION
The Euphorbiaceae are one of the largest and most diverse Angiosperm families in Mexico.In terms of number of species, they probably rank fifth, behind only the Asteraceae, Fabaceae, Orchidaceae, and Poaceae .Although members of the family reach their greate st di versity in dry tropical regions, they are distributed throughout the country in nearly all types of vegetation, from near sea level to we ll o ver 3000 m.The family ha s a high incidence of narrowly restricted tax a, and scores of spec ies are kno wn from a single collection or locality.It is not surprising then, that as neglected areas are more thoroughly botanized, many new species continue to be found .In 1995 and 1996, while collecting in Morelos and the sierr a of central Nay arit, I encountered by cha nce apparently undescribed taxa of Croton L. and Euphorbia L. Also, material of two other species of Croton was given to me by Mi chael F Wilson, Drylands Institute , Tucson, Arizona, for study and identification.Because attempts to match these collections to any known taxa have proven unsu ccessful, they are here described as new.
Euphorbia nayarensis is a member of subgenus Agaloma (Raf.)House section Cyttarospermum Boiss.In habit, it superficially resembles E. guadalajarana S. Watson.However, that species possesses distinctly peltate leaves, long spreading trichomes on the involucres, filiform divisions of the involucral appendages, and entire styles.The affinity of E. nayarensis appears to be with E. soobyi McYaugh, a narrow endemic known only from high elevations in the Sierra de Cuale, Jalisco, and the two species are nearly identical with respect to characters of the seeds and involucres.The leaves of E. soobyi are ovate to oblong-elliptic, and this characteristic serves to distinguish it from E. nayarensis.
Nayarit: Mpio.Nayar, along the road from Ruiz to Mesa del Nayar, 2.5 kIn (by road) northeast of EI Maguey, 22°07'34"N, 104°48' 14"W, ca.1300 m, 13 Oct 1996, Steinmann 1050 (holotype RSA; isotypes ARIZ, MEXU, MICH).Monoecious perennial herb to subshrub reaching 20 cm high, from a persistent taproot, woody branches reddish brown to gray brown, the whole plant covered with a stellate indumentum, the rays of the trichomes to 1.5 mm long but usually shorter; stipules reduced, often apparently absent, when present represented by ca.2-5 minute, narrowly cylindrical, yellow to brown glands ca .0.2 mm long; leaves alternate, with petioles 0 .2-1.1 cm long, a pair of conical, cupuliform glands ca.0.2 mm long and 0.2-0.3mm wide usually present on the abaxial surface of the petioles just below its point of attachment with the lamina, the lamina oblong, elliptic, or ovate, 3-nerved from the base, 0.6-2.6 cm long, 0.5-1.4cm wide, upper surface stellatevillous, olive green, lower surface stellate-Ianate, whitish, rounded to oblique at the base, subacute to rounded at the apex, the margin entire to shallowly serrate with inconspicuous teeth to 0.3 mm long and spaced ca .I mm apart; inflorescences bisexual, axillary or terminal, 0 .7-2.5 cm long, with 1-4 pistilIate flowers at the base and up to ca. 25 staminate flowers distally; bracts subulate, 0.7-1.1 mm long , each side of the base subtended by a group of 2-5 glands similar to those of the stipules; staminate flowers on pedicels 1.3-3.1 mm long, calyx lobes 5, united towards the base, their free lobes deltoid, acute, 0 .9-1.1 mm long, the petals 5, white, narrowly oval to oblong, 1.2-1.7 mm long, the receptacle densely villous, the stamens II, filaments glabrous, 0.6-1.7 mm long, anthers elliptic, 0.4-0.6 mm long, basifixed; pistillate flowers subsessile or on stout pedicels to 0.5 mm long, calyx lobes 5-6, adaxial lobes reduced, subulate to narrowly triangular, acute, 0.8-2.1 mm long, abaxial lobes well developed, linear to obovate to spathulate, 2.6-6.7 mm long, subacute to rounded at the apex, petals absent, the ovary nearly globose, very shallowly 3-lobed, stellate-hispid, the longer rays of the trichomes to 1.5 mm long, the styles 3, united at the base, bipartite, the divisions filiform, rust brown, minutely papillate, 1.3-2.2mm long, sometimes bearing scattered stellate trichomes; capsules 3.2-4.1 mm in diameter; seeds elliptic to oblong, 2.7-3.4 mm long, 2.0-2.3 mm wide, dorso-ventrally compressed, shallowly foveolate, shiny, mottled black-gray, with a fleshy, cream-yellow, reniform caruncle 0.3-0.7 mm long, 1.2-1.5 mm wide.Open oak scrub on red , coarse, rocky volcanic soil with Croton pedicellatus H .B .K .and C. repens Schltdl.; known only from the type locality where the plants are common.The coarse red volcanic soil at the type locality is essentially the same soil on which I have observed the closely related Croton martinianus V.W. Steinm. in Sonora to be mo st common.The specific epithet honors Leonardo Varela Espinosa, a re-searcher at the Centro de Ecologfa of the Universidad Nacional Autonorna de Mexico in Hermosillo, Sonora, whose help with fieldwork in western Mexico I greatly appreciate.

Croton varelae
Based on the serrate leaves with petiolar glands, clusters of bottle-shaped glands subte ndi ng the bracts, and unequal pistillate sepals, Croton varelae is assignable to section Geiseleria (Klotzsch) Baill.as defined by Webster (1993, p. 812).There are about 15 species in this section, eight of which occur in Mexico.Four (c.cupulifer McVaugh, C. martinianus, C. chamelensis Lott, and C. varelae) are endemic to Western Mexico and collectively known from fewer than a dozen localities.One species, Croton ramlllatus Croizat, consists of two varieties, both of which are uncommon and restricted to southern Mexico.The other three species (c.glandulosus L., C. hirtus L'Her., and C. trinitatis Millsp.) are widespread "weedy" taxa throughout the Neotropics.
The Mexican species of sect.Geiseleria can be distinguished as follows: I. Gl ands subtending the bra cts located at the ends of long s lender stipes. .Variety magniglandulifer occurs in tropical deciduous forest in Morelos and Guerrero at elevations from 650 to ca. 1300 m; flowering and fruiting occur from June to October.A full description and illustration of this taxon (under the name var.insignilobis Croizat) is in Martinez (1995: 71-74).
As the name suggests, var.magniglandulifer differs from var. ramillatus by the much larger petiolar glands (0. 8-2.8 mm long, 0.7-1.6 mm in diameter vs. 0.1-0 .3mm long, 0.2 mm in diameter).In addition to this difference, var.magniglandulifer tends to have longer stipules.In her thorough treatment of the genus Croton in the state of Guerrero, Mex ico, Martinez (1995) treats this new variety as C. ramillatus var.insignilobis (Croizat 1945).Although I have examined only a limited amount of material, most of which is the same as that available to Croizat, I have doubts as to the validity of var.insignilobis.Croizat characterizes the pistillate flowers of var.ramillatus as having ca.7 sepals vs. 5 sepals in var.insignilobis.He also mentions that the capsules of var.insignilobis appear to be slightly larger.However, many of the collections I have examined that were referred to as var.ramillatus by Croizat (including Purpus 8450, an isotype, UC) actually have five sepals, and the difference in capsule size is slight.There does appear to be a difference in sepal shape, those on the type of var.insignilobis are broader, but this variation does not appear significant.
Craton ramillatus has previously been placed in sect.Cascarilla Griseb., but the distinctly unequal sepals of the pistillate flowers and the clusters of small glands at the base of the bracts suggest that it is better accommodated in sect.Geiseleria.
This species is very similar to Croton yecorensis V.W. Steinm.& Felger, a narrow endemic known only from the vicinity of Yecora, Sonora, and I believe that the two are closely related.They are identical in most features, and C. michaelii significantly differs only in possessing a lepidote indumentum and in lacking conspicuous stipitate glands, although minute stipitate glands can be present on the bracts and pistillate sepals.Aside from their putative relationship to each other, these species are taxonomically isolated and lack obvious affinities with other members of Croton.Even sectional placement is not clear at this time, This species is named in honor of Michael F. Wilson, entomologist and botanist, who has made significant contributions to the knowledge of the biota of the southwestern United States and northwestern Mexico.
The known localities of Croton disjunctus are separated by more than 600 km, but this species possibly also occurs in intervening Durango and Zacatecas.Despite the geographic disjunction, the plants are strik-ingly similar.The only variation that I have observed is that the leaves on the Chihuahuan plants possess petiolar glands, but these are lacking on the leaves of collections from Aguascalientes.The possession of petiolar glands is often a defining characteristic of sections within Croton (Webster 1993), and it is therefore interesting that this condition varies in Croton disjunctus.Due to the current paucity of material, how- ever, I cannot determine how consistent this difference may be or its potential taxonomic significance.
This species appears to be most closely akin to Croton fruticulosus Torr., a Chihuahuan Desert species ranging from Arizona to Texas and Tamaulipas.The known localities of C. fruticulosus in Chihuahua are in the eastern part of the state while that of C. disjunctus is in the southern portion.Croton disjunctus is distinguished from C. fruticulosus by its glabrous, evident (vs.pubescent, nearly obsolete) stipules and the multifid (vs.bifid) styles.In addition, Croton fruticulos us apparently never possesses petiolar glands.