Psacalium villosum Villaseñor, Hinojosa & Redonda-Mart., 2018

Villaseñor, José Luis, Hinojosa, Oscar & Redonda-Martínez, Rosario, 2018, A new species of Psacalium (Asteraceae, Senecioneae) from the state of Guerrero, Mexico, Phytotaxa 345 (1), pp. 73-77 : 74-76

Psacalium villosum Villaseñor, Hinojosa & Redonda-Mart. , sp. nov. ( Figs. 1 − 2 ).

Type:— MEXICO. Guerrero: Municipio de Chilpancingo , Rincón de la Vía, en una ladera pedregosa orientada al Oeste, cubierta de rocas cristalinas y selva mediana subcaducifolia, muy perturbada por los hombres y el ganado, crece a pleno sol, 900 m, 17° 17’ 15’’ N, 99° 28’ 55’’ O, 27 October 1959, H. Kruse 70 (holotype: MEXU!; isotypes: MEXU!; FCME!) .

Subscapose perennial herbs from a short woody caudex, covered with wooly and tawny trichomes, 80 − 150 cm tall. Roots fleshy, fibrous. Stems single, ramified at inflorescence, erect, terete, up to 1.5 cm in diameter, sulcate, glabrous or sparsely puberulent, with pith. Basal leaves forming a rosette, blades orbicular, 18.2 − 31.5 × 20 − 30 cm, centrally peltate, with 7 − 8 radiating lobes and veins, the lobes about 1/2 to 1/3 the distance to the center, the primary ones 5.5 − 7.0 cm long, each sinuately 2 − 3-lobed, adaxial surface sparsely pilose along veins, otherwise glabrous, margins ciliated, abaxial surface glabrous, veins pinnately subdivided; petioles 18–37 cm, dilated and sheathing at base, terete, striated, glabrous or scarcely puberulent. Cauline leaves alternate, the lowermost similar to the basal ones and about as large; upper cauline leaves progressively smaller, the blades palmately 3 − 5-lobed, the entire uppermost leaves are like large ovate bracts, 5 − 6 mm long, subtending the inflorescence, with adaxial surface glabrous or puberulent and abaxial surface softly pilose to short velutinous, membranaceous, the rudimentary apical blade puberulent, 2 × 2.5 mm, palmately veined. Capitulescence thyrsoid, 20 − 24 × 10.0 − 11.5 cm, composed of (15 −)20 − 60 heads, the branches and peduncles densely villose with up to 4 mm long crisped, septate hairs, intermixed with numerous shorter septate glandular-stipitate hairs. Heads discoid, 1.7 − 2.7 × (1.2 −) 1.9 − 3.1 cm; calyculate bracts 2 − 3, very inconspicuous, linear-lanceolate, 8.8 − 9.9 × 1 mm; capitulum peduncles 0.8 − 6.6 cm long; involucre campanulate to hemispheric, 1.3 − 1.5 × 1.5 − 2.4 cm; involucral bracts 14 − 20, imbricated in one or two series, oblong-lanceolate to linear-lanceolate, apices acuminate, 13.0 − 14.5 × 1.5 − 2.8 mm wide, greenish, conduplicate, quilled, densely glandular-stipitate on abaxial surface, and also with non-glandular septate trichomes, pilose-penicillate at apex; receptacle slightly convex, glandular-stipitate among the scars, 5.0 − 7.0 mm diameter. Florets 35 − 44 per head, perfect, fertile; corolla (9.0 −) 11.2–13.5 mm long, glabrous, whitish, yellowish-white or greenish-white, with a narrowly 7 − 11 mm long cylindrical tube and ascending or spreading, narrowly triangular 3.8 − 5.0 × 0.7 mm long lobes, subulate, papillose, the throat short, campanulate, 1 × 1 mm; anthers 2.8 − 3.0 mm, fully exserted at anthesis, rounded at base, with obtuse or oblong-lanceolate 0.6 − 0.8 mm long appendages, filaments 2.5 − 3.0 mm long; style 9.8 − 11.0 mm long, the branches 2.2 − 3.3 mm, flattened, recurved, obtuse, truncate, hispidulous on adaxial surface and apex, abaxial surface papillose. Cypselae columnar, 3.1 − 4.3 × 0.8 mm wide, terete, 17 − 18 ribbed, attenuate near apex and then lightly expanded, at base with a subcylindric carpopodium, ribbed, light brownish, glabrous; pappus of two series of 71 − 95 white, antrorsely-spiculated, flattened 8.0 − 11.6 mm long bristles.

Etymology:—The epithet refers to the most distinctive feature of the new species, the villose indument of the capitulescence branches, peduncles, and involucral bracts.

Conservation Status:—According to IUCN (2017), Psacalium villosum must be considered Vulnerable B2a largely due to its restricted distribution; this species is known only from three localities in a relatively well studied region.

Distribution and habitat:— Psacalium villosum appears to be restricted to a small area in the mountainous region of the Sierra Madre del Sur, in central Guerrero, Mexico ( Fig. 2 ). The species occurs on limestone slopes with clay soils, and in tropical deciduous forest, oak forest, pine-oak forest, and riparian vegetation, at elevations of 730 − 905 m.

Phenology:—Flowering occurs in October and November and fruiting probably in late November and December.

Additional specimens examined (paratypes):— MEXICO. Guerrero: municipality of Chilpancingo, 5.2 km al O del Ocotito, camino a Jaleaca , 735 m, 10 November 1982, R. Torres et al. 1797 ( MEXU!, RSA!) ; R. Torres et al. 1845 ( MEXU!, RSA!) ; Rincón de la Vía, al N de Rincón Viejo, 802 m, 17°18’31’’ N, 99°28’50’’ O, 29 October 2004, L. Lozada & J. Rojas 2688 ( FCME!, MEXU!, TEX!, XAL!) ; Rincón de la Vía, al N de Rincón Viejo, 905 m, 17°18’29’’ N, 99°28’38’’ O, 29 October 2004, L. Lozada & J. Rojas 2692 ( FCME!, IEB!, K!, MEXU!) .

Discussion:— Psacalium villosum is distinctive by the conspicuous villose indument of the capitulescence axis, branches, and peduncles ( Fig. 1 ). The villose trichomes are septate and up to 6 mm long; they are intermixed with large (up to 4 mm long) glandular-stipitate trichomes. Moreover, the heads of this new species are broad and bear many florets, usually between 36 and 44 florets per head. Another distinctive characteristic of P. villosum is its receptacle, which bears glandular-stipitate trichomes among the scars. Furthermore, this new species lacks the capitulescence bracts and the conspicuously calyculate heads which are typical characters of Psacalium species.

The most similar species to Psacalium villosum is P. peltatum (Kunth) Cassini (1826: 461) . Both are alike in habit and leaf morphology. Among the three varieties recognized of the latter, P. peltatum var. conzattii (B.L. Rob. & Greenm.) Pippen (1968: 427) also has a mixture of glandular and non-glandular trichomes on the capitulescence branches and has heads that can bear up to 40 florets. However, the capitulescence of P. peltatum var. conzattii does not have such a dense and conspicuous yellowish villose indument as P. villosum ( Fig. 1 ). Moreover, the capitulescence branches of the former are conspicuously bracteate and its heads are noticeably calyculate. Other species that are somewhat similar in habit, and leaf and capitulescence morphology to P. villosum are P. eriocarpum (S.F. Blake) Blake (1938: 492) and P. matudae Robinson & Brettell (1973b: 261) . The former is endemic to the Mexican state of Jalisco ( McVaugh 1984) and the latter is only known from the State of Mexico ( Robinson & Brettell 1973b). Both species have a thyrsoid capitulescence, but their branches are clearly bracteate and their heads are conspicuously calyculate. Moreover, their capitulescence branches are pilose (or have coarse setae in P. matudae ), but are not densely yellowish villose as in P. villosum . Furthermore, they have smaller heads with fewer florets, usually 6–12 per head in P. eriocarpum , and about 11 in P. matudae . Finally, P. eriocarpum and P. matudae have pubescent instead of glabrous cypselas.

Figures

FIGURE 1. Holotype of Psacalium villosum housed at the National Herbarium of Mexico (MEXU).

FIGURE 2. Known geographical distribution of Psacalium villosum in the state of Guerrero, Mexico.