2003 - Brief description

BASIONYM: Phragmipedium xerophyticum Soto Arenas, Salazar & Hágsater, Orquídea (Méx.) 12(1): 2-6, 1990 (TYPE: MEXICO, Oaxaca: jungles on the slopes of the Gulf of Mexico, 320 m a.s.l., xerophytic vegetation of Agave, Beaucarnea, Bursera simaruba, Plumeria and Pseudobombax ellipticum, in a karstic zone surrounded by high evergreen jungle and tropical oak forests; September 6, 1988, G.A. Salazar 3740, M. Soto, E. Yañez & H. Hernández, holo. AMO[ill. voucher]!; iso. K!).

SYNONYM: Paphiopedilum xerophyticum (Soto Arenas, Salazar & Hágsater) VAAlbert & B6rge Pett., Lindleyana 9(2): 137. 1994.

Plant that spreads vegetatively and consists of fan-shaped shoots connected by elongated rhizomes, 15-20 cm high, up to 1 m2.

Roots simple, whitish-brown, glabrous with hairs in the attachment zone, starting from the base of the shoot, up to 0.8 mm thick.

Rhizome conspicuous, elongated, straight, brittle, 1-2 mm thick, 3-8(-20) cm long between the contiguous shoots; with 5-12 scarious, brown, tubular to obtuse- or acute-angled, mucronate leaf sheaths, 6-9 mm long.

Shoots formed from 5-8 leaves, 3-12 cm high, 6.5-13 cm wide.

Leaves two-lined, lanceolate-oblong, apex unequal, blunt, crenate, incised, leathery-fleshy, very stiff, light green, basal leaves small, gradually larger, 3.5-12 cm long, 1.2-1.8 cm wide, 1 mm thick.

Inflorescence terminal, with 2 internodes, flower panicle of two racemes (rarely simple), hairy, many-celled hairy, reddish-brown; 6.5-13 cm high, 1-1.3 mm thick; with a bract near the middle of the stem, tubular, roundish to caudal, yellowish, hairy, 8-15 mm long;

Rhachis very short with about 3-7 consecutive flowers, only one flower open at a time, about 12-15 mm long;

Floral bracts imbricate, distichous, conduplicate, cymbiform, caudate, recurved apex, brown, hirsute, 4-5 x 5 mm.

Ovary unilocular, with parietal placentation, trigonous, pubescent, pinkish, 27-28 mm long, 1.5 mm thick Pedicel short, rigid, hirsute, subtrigonous, 2.5-3 mm long, 0.8 mm thick.

Pedicel short, rigid, hirsute, subtrigonous, 2.5-3 mm long, 0.8 mm thick.

Flower deciduous, small, unscented, 13-25 mm tall, 15-20 mm wide, white fading to pink, weakly textured.

Sepals valvate, adaxial surface glabrous, the abaxial one pubescent, hairs septate; the dorsal sepal directed forward, elliptic, acute-subacute, mucronate, concave, 9-14 x 5-6.5 mm; the two lateral sepals usually fused completely into a descending, suborbicular, obtuse, bifid, mucronate, concave, 8-9.5 x 8.5-12 mm synsepal.

Petals linear-banded, pointed, arched, glabrous, ciliate at the base, 11-15 x 2.5-3 mm.

Labellum calceolate, subglobose, inflated, slightly sulcate along veins in orifice area, very delicate texture; outer surface glabrous, the inner surface conspicuously hirsute near base, with the glandular, multicellular, bright purple hairs continuing along midline; basal margins (around exit orifice) erect, somewhat reflexed and thickened; apical margin incurved; entrance orifices small, ovoid, ca. 2 x 3 mm; lateral lobes small, incurved, broadly triangular, subacute, without thickening at margins, nor projections (horns), nor forming hollow gibbous regions, adherent to each other ca. 3 mm, well delimiting entrance and exit orifices; labellum surface without “windows” or transparent areas; total length of labellum 10-14 mm, 6-8 mm high, 7-9 mm wide.

Column short, gynoecium and androcecium fused only 1-2 mm.

Stigma arcuate, descending, fleshy and massive, the body approximately trigonous, horizontal surface in front of the staminode with multicellular trichomes; the apex of the body deflexed and longitudinally sulcate; stigma lobes apical, laminar, thickened; 4-5 mm long, 1-1.3 mm at widest part.

Androcecium with 2 fertile stamens and a petaloid staminode.

Staminode conspicuously pedunculate ca. 1 mm, convex, broadly trilobate, apex subacute and rounded, longitudinally sulcate and glabrous, violet or purple; with an axial keel on the inner surface, with 2 clusters of long, multicellular, multicellular, long hairs. multicellular, long, bright purple hairs along the keel; lateral lobes spreading and deflexed, subquadrate, with the margins slightly reddened; ca. 3 x 4.5 mm.

Anthers 2, pedunculate, filament recurved, fleshy, theca ovate-triangular, somewhat cordate, acute or obtuse, fleshy, white, apex directed downward and outward; ca. 1 mm long.

Pollinia 2 in each anther, adhering to each other, forming an oval, bevelled structure, granular, yellowish, 0.5 x 0.4 mm.

Capsule fusiform-subcylindrical, 3-carinate, ca. 2.5 cm long, 0.4 mm thick.

Chromosome count 2n = 26.

DISTRIBUTION: Endemic; in the Atlantic watershed of the Tehuantepec Isthmus, in Oaxaca.

ECOLOCY: Rupiculous on limestone outcrops with xerophytic vegetation, surrounded by rainforest and warm oak forest, at 320 m elevation. Flowering in the summer.

RECOGNITION: The monotypic genus Mexipedium is recognized among the Cypripedioid orchids by the fleshy-coriaceous leaves, the very small flowers (ca. 2 cm diameter), unilocular ovary, branched inflorescence, valvate sepal aestivation, and inflated lip. Mexipedium is, doubtless, the most exciting discovery of the last years in Mexican Orchidaceae, and it has been subject of much research. Its initial placement in Phragmipedium highlighted conflicts in the generic circumscription of the conduplicate Cypripedioids. Morphological and molecular data place Mexipedium sister to Phragmipedium, and most authors consider that it warrants generic rank.

CONSERVATION STATUS Endangered. Despite searching in similar habitats, only a single population of few specimens has been located so far. The locality is subject to disturbance.

EXAMINED SPECIMENS: OAXACA: Salazar 3742 et al. US! Hernández 1602 CHAPA!