Villadia laxa, A NEW SPECIES FROM NORTHWEST MEXICO


Reid Moran and Charles H. Uhl


Of the rather few botanist who have got­ten well into the mountains of northwest Mexico in the last fifty years, several have found a distinctive unknown species of Vi­lladia in Sonora and Sinaloa. Because the genus was poorly understood, their collec­tions have remained unidentified. With re­cent progress in the genus, however, it is now clear that this collections represent yet another unnamed new species; and we seize this opportunity to remedy this deplorable situation. The type collection was made 17 years ago by Myron Kimnach and Hernando Sánchez Mejorada on the road from Choix, Sinaloa, to San Vicente, Chihuahua. It is the only collection to have a chromoso­me count, which is so useful in this genus. The description and the photograph are of dried specimens, so we look forward to seeing someday what the real live plants look like.


Villadia laxa Moran and Uhl, spec. nov.

Pachyphytum sp. H. S. Gentry, Río Mayo Pl, p. 118. 1942 (Based on Gentry 639)


Herba glabra 1-3 dm alta, caulibus scabris, foliis subulato-lanceolatis. Thyrsus laxus 10-30-ramosus, floribus cincinno 2-7 mm separatis. Corolla aperta 4-6 mm lata. Folliculi erecti 3 mm alti, stylis gracilibus 0.8 mm longis excurvatis. Typus: Kimnach et Sánchez Mejorada 2091, HNT. Species cau­libus scabris thyrsis laxis floribus apertis folliculorumque forma V. minutiflora et V. squamulosa proxima; differt a priore foliis sepalisque glabris (in illa ciliatis), a posteriore nectario oblongo parviore (in illa flabelliforme), ab ambabus basi perenni altiore chromosomatumque numero distincto.


Glabrous but papillose herb, with one or a few erect annual flowering branches that die back to short perennial base; this stem base to 6 cm high and 6 mm think, from cross-striated tuberous root to 12 mm thick or with cluster of carrotlike roots to 5 mm thick. Flowering stems 1-3 dm high, 1-3 mm thick, papillose-roughened at least above, still leafy above at anthesis, bare by Fe­bruary but with densely leafty new shoots at base and to 5 cm above; leaf scars oval, 0.5-1 mm wide. Leaves crowded towards base, more scattered above, grayish, subulate, lanceolate, subacute, spurred at base, papi­llose at apex, 0.5-3.5 cm long, 2-4 mm wide. Inflorescence a raceme or lax thyrse 5-20 cm high and 1-2.5 cm wide (sometimes also with a few smaller axillary ones below), with 10-30 branches, each a lax cincinnus 0.5-3 cm long, with peduncle to 10 mm long and with 1-4 sessile or short-pedicelled flowers 2-7 mm apart on cincinnal axis; pedicels ca. 0.5 mm thick, the terminal ones (pseudo-pedi­cels) to 2 mm long. Calyx cuplike, 4-5 mm wide, the sepals free to base and spurred, erect, subequal, lanceolate, subacute, papi­llose at apex, 2.5-3.5 mm long, 1-1.5 mm wide. Corolla pale rose with lighter margins, drying brown with whitish margins, 3 mm long, open and 4-6 mm wide, the tube ca. 1 mm long, the segments ovate, acute, 1.5-2 mm wide, papillose keeled, with subapical mucro ca. 0.2 mm long (BH). Stamens erect, the filaments 1.5 mm long, the anthers ca. 0.4 mm long. Nectar glands reddish in dried specimens, ca. 0.7 mm wide and 0.25 mm thick at apex. Gynoecium ca. 1.5 mm thick and 2.5 mm high, with styles ascending, ca. 0.5 mm long. Fruit ± jug-shaped, ca. 3 mm high, ca. 3 mm wide below and 1.5-2 mm wide above (exclusive of styles), the folli­cles red-brown, vertically gibbous above, the suture erect in lower 3/4, outcurved abo­ve throught ca. 60°, with outcurved styles ca. 0.8-1.0 mm long.


Seeds red-brown, ovoid, ca. 0.6 mm long, papillose in rows. Chromosomes: n=14 (U2528). Flowers Oct.-Nov.



Fig. 19.- Type specimen of Villadia laxa (HNT), from near La Paridia, Sinaloa, grown at the Huntington Botanical Gardens.


Type collection: With Mamillopsis senilis, Agave schidigera and Marina nutans, 29 miles east of Tasajera and 17 miles east of La Paridia, Sinaloa, México (near 26°46'N, 107°03'W), 1970 m, 8 November 1977, Myron Kimnach and Hernando Sánchez Mejorada 2091, HBG 39887; (Holotype HNT; isotype BH (Uhl 2528), US).


Distribution: Mountains of Sinaloa and Sonora at 1900-2300 m.


Collections: Sinaloa: With Alnus sp., Styrax argenteus, Mahonia sp., Prunus serotina, Clethra macrophylla, Pinus, Quercus, and Junglans, steep north slope at 6500 ft, 3 mi N of Los Ornos along road to Ocurahui, Sierra Surutato. Mcpo. de Badiraguato (?), 3 Nov. 1969. D. Breedlove & Kawahara 16926 (CAS); with Pinus, Quercus, and Ar­butus, steep cliff on east escarpment of Bufa de Surutato at 7500 ft, along road from los Hornos to Surutato, D. Breedlove 16468 (CAS); Bufa de Surutato, 7200 ft, D. Breedlove & R. F. Thome 18446 (RSA); 5 mi ME of La Cienega on road to Santa Rita, 7000 ft, Mpio. de Badiriguato (?), D. Breedlove & R. F. Thome 18596 (RSA). Sonora: Shady side of rock, Sierra des Papas, H. S. Gentry 639 (DS).


In an isotype of V. laxa Uhl found a ga-metic chromosome number of n = 14. In subgenus Villadia he has otherwise found this number only in V. aff. diffusa Rose, of Oaxaca and Guerrero, a plant that does not appear closely related.


The species is named for the open thyrse, with flowers commonly separated in the cincinni, the uppermost conspicuosly pseudo-pedicellate.


This is in contrast to the rather dense thryrse, with more crowded branches and more compact cincinni, in such species as V. cucullata Rose and V. misera (Lindl.) Clau­sen. However, the inflorescence is somewhat similar in V. minutiflora Rose of Oaxaca and in V. squamulosa (S. Wats.) Rose, of Wes­tern Texas to Chihuahua and northern Zacatecas. These two species also have the stems to some degree papillose-roughened, have small open corollas, and have pistils and follicles similar in form; and they are probably its closest relatives. Villadia minutiflora (n = 21) is a somewhat smaller plant with herbage ± puberulent and leaves and sepals stiff-ciliate; and V. squamulosa (n = 17), with a less consistently open thryse and less roughened stem, is distinctive in the genus in its relatively large flabellate nectar glands. For each of these three species, the chromosome number is known from only one or (in V. squamulosa) two counts.


VERSIÓN EN ESPAÑOL

Entre los pocos botánicos que han recorrido las montañas del NW de México en los últimos 50 años, varios han encontrado una especie característica y desconocida de Villadia, en los estados de Sonora y Sinaloa. Debido a que el género estaba pobremente conocido, sus colectas habían permanecido sin identi­ficar. Con los avances recientes en este género queda claro que estas colectas representan una nueva especie sin nombre y nosotros tomamos la oportunidad de remediar esta lamentable situación. La colección tipo fue hecha hace 17 años por Myron Kimnach y Hernan­do Sánchez Mejorada en el camino de Choix, Sinaloa a San Vicente, Chihuahua y es la única con cuenta cromosómica, la cual es tan útil en este género. La descripción y la fotografía son de especímenes secos. La descripción de Villadia laxa puede ser seguida fácilmente en el texto en inglés.


Uhl encontró en un isotipo de V. laxa un número cromosómico gamético de n = 14. En el subgénero Villadia él ha hallado este número solamente en V. aff. diffusa Rose, de Oaxaca y Guerrero, una planta con la que no parece estar relacionada estrechamente.


La especie fue llamada así por su tirso abierto, laxo, con flores comúnmente separadas en los cincinos, las más superiores conspicuamente pseudo-pediceladas. Esto en contraste con el más bien denso tirso, con ramas más amontonadas y cincinos más compactos de especies tales como V. cucullata Rose y V. misera (Lindl.) Clausen. Sin embargo, la inflorescencia es algo similar a V. minutiflora Rose de Oaxaca y a V. squamulosa (S. Watson) Rose, del occidente de Texas a Chihuahua y norte de Zacatecas. Estas dos especies también tienen los tallos áspero rugosos en cierto grado, con peque­ñas corolas abiertas y pistillos y folículos semejantes en su forma, y probablemente son los parientes más cercanos. Villadia minutiflora (n=21) es una planta algo más pequeña con follaje más o menos puberulenta y hojas y sépalos rígidamente ciliados; y V. squamu­losa (n = 17) con un tirso abierto menos consistente y tallo menos áspero, es distintiva en el género por sus relativamente grandes nectarios flabelados. En cada una de estas 3 especies, el número cromosómico es conocido solamente por una o (en V. squamulosa) dos cuentas.


© Cactáceas y Suculentas Mexicanas, 1995