Phaseolus texensis is a new species known only from rocky canyons of the eastern and southern Edwards Plateau of central Texas. Morphological examination and field observations, in conjunction with current molecular phylogenetic analyses based on nuclear ribosomal and chloroplast DNA sequences and a discrete and limited geographical range, support the taxonomic recognition of this species, which is accordingly described and illustrated here.
During the course of a taxonomic revision of Phaseolus for the Flora of North America (Delgado-Salinas, in prep.), it became evident that plants from the botanically relatively well-known central part of Texas represent taxonomically problematic populations meriting further study. One herbarium specimen from this area (V. L. Cory 52444 CAS-DH) was annotated in the first half of the last century by Oliver W. Norvell as Phaseolus pedicellatus var. scabrellus ined. (Section Pedicellati Freytag). Subsequently, Delgado-Salinas (1985) hypothesized these plants to be atypical forms of P. polystachios (L.) Britton, Sterns & Poggenb., a species of the eastern U.S.A. Recently, Freytag and Debouck (2002) identified two herbarium specimens from this area as P. polystachios subsp. smilacifolius (Pollard) Freytag (Section Paniculati Freytag), pointing out, however, that the plants concerned were anomalous in this taxonomic placement. Apparently, Debouck (in Freytag & Debouck, 2002) was of the opinion that these plants would be better referred to another species. This has lead to consternation, particularly for workers not conversant with this group.
Examination of more herbarium material and of populations in the field reveals that these plants are morphologically closer to those of section Pedicellati Freytag, and that they appear to represent a morphologically distinct taxon allopatric to all other species of Phaseolus. In addition, in a phylogenetic analysis of Phaseolus (Delgado-Salinas et al., 2006) based on combined sequence data of nrDNA (ITS) and cpDNA (trnK/matK), two accessions of P. texensis were established in a clade with 100% bootstrap support as sisters to a larger group of species (Fig. 1). This clade, named the Pedicellatus group, comprises all species of sections Pedicellati and Digitati Freytag, along with a species of section Paniculati (Delgado-Salinas et al., 2006; Mercado-Ruaro et al., in press). Conversely, there was no support for the placement of P. texensis within the clade that comprises species of section Paniculati (i.e., Phaseolus polystachios), included in this analysis in the Lunatus and Polystachios phylogenetic groups (Fig. 1). Thus, the combination of morphological, distributional, and molecular evidence strongly supports the recognition of these central Texas populations as a separate, narrowly endemic species, placed in a rather enlarged but well supported section Pedicellati (Delgado-Salinas et al., 2006). Within the Pedicellatus group, this new species is sister to accessions of north and central Mexico, and to the geographically closer P. grayanus Wooton & Standl., inhabiting the Chihuahuan Desert region of northern Mexico, Trans-Pecos Texas, southern New Mexico, and southeastern Arizona.
TYPE: UNITED STATES. TEXAS. Kerr Co.: E side of St. Rt. 16 at foot of switchbacks on ridge separating Guadalupe and Medina watersheds, 3.2 road miles S of Turtle Creek bridge S of Kerrville, Fall Creek Quadrangle, at N 29°55′24.5″, W 099°14′15.2″, elev. 1180–1900 ft, 29 Oct 2005, W. R. Carr et al. 24232 (TEX) (Holotype: TEX!; Isotype: MEXU!).
Phaseolus grayanus Wooton & Standley affinis, sed differt petioliis, inflorescentiis axe, pedicellis pilis uncinatis (vs. plerumque numerosis pilis recti vel curvi antrorsis), bracteolis 0.5 mm (vs. 1.0 mm), fructibus 5–6(7) (vs. 4–5(6)) seminibus.
Herbaceous perennial Vines, trailing or climbing up to 7 m long, from tuberous taproots. Stems terete, striate, lignescent at maturity, sparsely beset with hooked and retrose hairs. Leaves with axillary buds sometimes developed at the base of the inflorescence; stipules lanceolate, 1.5–3.0 mm long, 0.8–1.2 mm wide, acute at tip, 3-veined, ascending to reflexed; petioles and rachises canaliculate, sparsely covered with hooked hairs; petioles 1.0–5.0 cm long; rachises 0.7–1.7 cm long; stipels subulateobovate, 1.0–2.5 mm long, ascending on terminal pulvinus and spreading on lateral pulvini; leaflets membranous to slightly chartaceous, terminal leaflets ovate to broadly so, occasionally round to quadrate lobed at base, 2.0–8.5 cm long, 2.0–7.0 cm wide; lateral leaflets ovate, sometimes basally lobed, acute at tip, apiculate, 1.5–7.0 cm long, 2.2–4.8 cm wide, rounded to subtruncate at base; upper and lower surfaces of leaflets sparsely covered with hooked hairs intermixed with antrorse-curved hairs. Inflorescences of pseudoracemes, often minute secondary axes or stalks developed on floral nodes, main axis usually covered with hooked hairs; peduncles 5.0–10.0 cm long; rachises up to 12.0 cm long, with 5–13 floral nodes, each 2–3 flowered, often the middle one on a short stalk; primary nodal bracts triangular, 1.0–2.0 mm long, ca. 0.8 mm wide, 3-veined, persistent; secondary nodal bracts oblong, ca. 1 mm long, usually caducous; pedicels 4–9 mm long, sparsely covered with hooked hairs, arcuate in fruit; bracteoles ovate, ca. 0.5 mm long, 1-veined, persistent. Calyces campanulate, 2.5–3.5 mm long, ca. 2.5 mm broad; inner surface covered with appressed hairs in the tube, outer surface with minute hooked and straight hairs on the lobe margins; upper lobe emarginate, laterals and lower lobes triangular, ca. 1.0 mm long. Corollas pink fading to dark pink, 1.2–1.5 cm long, ca. 7.0 mm high; standards oblong to orbicular, ca. 1.2 cm long, ca.1.0 cm wide, emarginate at apex, glabrous, lamina thickened at point of flexure, toward the base on both sides of claw bearing two flap-like appendages, tongue-guide surface concave and papillose, basal claws ca. 1.0 mm long; wings obovate, 1.2–1.5 cm long, ca. 8.0 mm wide, constricted toward base, upper basal margin folded and thickened, round-auriculate, claws ca. 4.0 mm long; keels 6.5–9.0 mm long, ca. 6.0 mm high, 1½ closely-coiled diameter ca. 2.0 mm across, twisted and facing forward, transverse pouch ca. 1 mm long, claws of keel ca. 4.0 mm long. Androecium with vexillary stamen ca. 1.0 cm long with a globose appendage toward the base; staminal tube ca. 1.5 cm long, biauriculate toward the base, with 4 dorsifixed and 5 basifixed anthers, these oblong, ca. 0.6 mm long. Pollen tricolporate, often with pseudocolpi, subtectate, finely reticulate. Gynoecium with nectary disc ca. 1.0 mm long; ovary linear, ca. 6.0 mm long, sericeous; ovules 5–7; style bearded introrsely; stigmas usually introrse; stigmatic pads oblanceolate, ca. 0.6 mm long. Fruits oblong, slightly falcate, 3.5–5.2 cm long, ca. 8.0 mm wide, short-beaked (2.0–3.0 mm), pendent, elastically dehiscent, compressed; valves chartaceous, strigose, expanding slightly over the 5–6(7) seeds. Seeds oblong, ca. 5.0 mm long, ca. 4.5 mm wide; hilum oblong, ca. 1.0 mm long, with epihilum; lens not prominent; halo black; surfaces smooth, brown mottled with black. Seedlings with hypogeal germination (or phanerogeal); epicotyl pilose, often red-pigmented; stipules entire to bifid; petioles with basal and apical pulvini; stipels minute; eophylls simple, ovate, obtuse to acute at tip, truncate or slightly lobed at base; next leaves trifoliolate. Chromosome number unknown.
Flowering and Fruiting: September through November.
Distribution and Habitat: Phaseolus texensis is restricted to the eastern and southern parts of the Edwards Plateau of Texas at elevations from 200 to 600 m. This species is usually found in small populations, in mixed woodlands, on limestone cliffs and outcrops, frequently along creeks. In Travis Co. this wild bean grows associated with Juniperus ashei J. Buchholz, Quercus buckleyi Nixon & Dorr, Ulmus crassifolia Nutt., Verbesina virginica L., Chasmanthium latifolium (Michx.) H.O. Yates, Desmodium paniculatum (L.) DC., Ruellia drummondiana (Nees) A. Gray, Ligustrum japonicum Thunb., Parthenocissus quinquefolia (L.) Planch., Rhamnus caroliniana Walter, Garrya lindheimeri Torr., Vitis sp., and Forestiera pubescens Nutt. In Kerr Co. it grows with Aster texanus E. S. Burgess, Brickellia cylindracea A. Gray & Engelm., Celtis reticulata Torr., Hamamelis virginiana L., Lindera benzoin (L.) Blume, Parthenocissus quinquefolia (L.) Planch., Platanus occidentalis L., Prunus serotina Ehrh., Quercus buckleyi, Q. laceyi Small, Q. muehlenbergii Engelm., Rhamnus caroliniana, Tilia americana L., Verbesina virginica L., and Vitis cinerea (Engelm.) Engelm. ex Millardet.
The species epithet alludes to the distribution of this species, which is endemic to the state of Texas.
Additional Specimens Examined: UNITED STATES. Texas. Bandera Co.: W-facing but rather mesic slope on E side of Williams Creek, ca. 500–1000 ft. N of Williams Creek Rd. crossing ca. 4.5–4.6 road miles N of jct. R. M. 470 at Tarpley, on Creveling Ranch, Tarpley Quadrangle, at N 29°42′19.3″, W 099°19′10.2″, elev. 1480–1500 ft, 16 Apr 2002 (sterile), W. R. Carr 20635 (TEX). Kerr Co.: 8.2 mi NE of Kerrville, 19 Sep 1937, V. L. Cory 24567 (GH); 13 miles southwest of Kerrville, frequent on steep limestone bank of Lamb Creek, 2 Oct 1946, V. L. Cory 52444 (CAS-DH); 9 mi SW of Kerrville, 13 Oct 1940, H. B. Parks 35738 (GH-2). Travis Co.: Tributary of Bull Creek emanating from Stillhouse Hollow, ca. 100–200 ft. upstream from (E of ) its confluence with Mayfield Creek, downstream from a trail crossing near conspicuous 20–30 ft N-facing undercut bluff, ca. 1200 ft SW off eastern of two intersections of Spicewood Springs Rd. and Loop 360. Jollyville Quadrangle, at 30° 22′55″ N, 97°46′06″ W, elev. 580 ft., 26 Sep 1995, W. R. Carr 14861 (TEX); 1 Oct 1995, W. R. Carr 14909 (TEX); 26 Oct 1995, W. R. Carr 15065 (TEX); same locality, 5 Oct 2005, T. L. Wendt & W. R. Carr 7379 (TEX). Uvalde Co.: Frio River, 30 Sep 1929, E. Normand s.n. (TEX-2).
Phaseolus texensis can be distinguished from P. polystachios (section Paniculati), with which it has been considered recently conspecific (Freytag and Debouck, 2002), by a basic difference in inflorescence structure. The inflorescences of P. texensis are pseudoracemes, while those of P. polystachios are contracted panicles with lateral branches developing along the axis of the inflorescence.
Phaseolus texensis is positioned in the section Pedicellati, because of the support from molecular data (Fig. 1), and to its morphological similarity with other species of this section. It is in many ways most similar to P. grayanus, but it differs in leaf form, density of vestiture, length of the bracts and bracteoles, and ovule number. The terminal or uppermost leaflets in Phaseolus grayanus tend to be mostly deeply tri-lobed, while those of P. texensis range from broadly ovate to slightly tri-lobed, not as dissected as in the former. Indument in P. grayanus tends to be more profuse than in P. texensis, especially distinctive by the presence of more ascending hairs on petioles, peduncles, and pedicels. Bracts and especially bracteoles are slightly smaller in P. texensis (bracteoles ca. 0.5 mm long) than in P. grayanus (bracteoles ca.1.0 mm long). Ovaries in P. texensis bear 5 to 7 ovules, whereas those of P. grayanus have 4 to 5 (rarely 6) ovules.
In addition, the habitat preferences of these two species are distinct. Phaseolus texensis grows on limestone soils in mixed woodlands at low to mid-elevations (200 to 600 m), whereas plants of P. grayanus occur on drier slopes or canyons in rich volcanic soils, among oak and pine-oak forests between 1600 to 2500 m.
Based on our field observations and herbarium specimens, Phaseolus texensis is a rather rare species that deserves protection, and therefore, considering human activities around the few localities where it has been collected, we recommend treating it as vulnerable.
Key to the species of Phaseolus section Pedicellati in Texas
1. Leaflets mostly tri-lobed, lobes commonly quadrate; inflorescence with 5–7 floral nodes; bracteoles ovatelanceolate, ca. 1.0 mm long; fruits 2.5–3.0 cm long, 4–5(6)-seeded; Chihuahuan Desert region of northern Mexico, Trans-Pecos Texas, southern New Mexico, and southeastern Arizona; elevations from 1600 to 2500 m P. grayanus
1. Leaflets mostly ovate to broadly ovate, occasionally lobed, lobes commonly round; inflorescence with 5–13 floral nodes; bracteoles ovate, ca. 0.5 mm long; fruits 3.5–5.2 cm long, 5–6(7)-seeded; eastern and southern parts of the Edwards Plateau of Texas; elevations from 200 to 600 m P. texensis
We are grateful to Tom Wendt, curator of the University of Texas at Austin Herbarium (TEX) for his uncompromising support both in the field and in the herbarium; to M. R. García Pen˜a (MEXU) for her assistance in obtaining loans of herbarium material, and to L. Torres-Colín and A. Wong for technical help. We are indebted to the curators of the cited herbaria for kindly providing specimens on loan; Albino Luna for the excellent line drawing; Fernando Chiang for providing the Latin diagnosis, and James Henrickson, Matt Lavin, and Billie L. Turner for their continuing support. Beryl L. Simpson, B.L. Turner, and two anonymous reviewers generously improved the manuscript. Partial funding of AD-S research by UNAM-DGAPA and by KLARF-Programme, Royal Botanic Gardens, Kew.