Hechtia melanocarpa L.B.Sm.
Literature references:
Comments:
- Detail from Utley & Utley in Syst. Bot. 13(2): 281-2. 1988
Hechtia rnelanocarpa is a conspicuous component of the vegetation near the type locality, Canon del Zopilote, in Guerrero, Mexico. Although H. melanocarpa is a robust species which forms large populations in this region, it has been collected only rarely. This may be in part a reflection of its large size and fiercely spiny leaves. Specimens we have observed and collected reach 3 m in height when in flower with leaves in excess of 1.5 m in length (Utley & Utley 7493, 7494, 7499). As recently as 1974 (Smith and Downs 1974), H. melanocarpa was thought to be known only from its type which consists of a leaf, a pistillate inflorescence with capsules, a lateral branch with flowers at anthesis, and habit photographs. Other collections of Hechtia from the type locality were either undetermined (Ogden 5112; Miranda 9306) or identified as H. stenopetala Klotzsch (Moore 5235) (Smith and Downs 1974). Because the type of H. melanocarpa (Foster 1258) is atypical of the species in its slenderly cylindric inflorescences with unusually short lateral branches (to only 9 cm), specimens of H. melanocarpa can not be correctly identified by using the most recent treatment of Hechtia (Smith and Downs 1974). All the individuals we observed in Guerrero or herbarium specimens available had pistillate inflorescences with lateral branches exceeding those observed on Foster 1258 (? 10-60 cm vs. 3.5-9 cm). Only ultimate lateral branches on these inflorescences approached those of the Foster collection in size. The depauperate inflorescence on Foster 1258 may be a reflection of the fact that the plant was flowering in cultivation. Although large in comparison to many other Hechtia species, the type of H. melanocarpa is at least 30% smaller than individuals observed at the type locality. From our examination of type material of H. melanocarpa and H. stenopetala and from our ongoing field work in Guerrero, it is obvious that Moore 5235, Odgen 5112, Miranda 9306, and Utley & Utley 7493 and 7494 are conspecific with H. melanocarpa. These collections have similar thick, leathery leaves which are glabrous above but lepidote beneath. Inflorescences on our collections are terminal like that reported for H. melanocarpa and have a similar white-flocculose pubescence. In form and size, floral bracts, sepals and petals of pistillate and capsular specimens available, closely correlate with that observed on, and reported for H. melanocarpa. Although the original description states that filaments are wanting, rudimentary stamens are evident on Foster 1258 and our collections. Capsules on Utley & Utley 7494 are similar in size to those on the type collection but would be characterized as ovoid, rather than slenderly ovoid. Since Foster 1258 flowered in cultivation, there may not have been sufficient pollen from other species of Hechtia or sufficient pollinators available to insure good seed set and normal capsule development.
Sexual dimorphism is clearly evident for inflorescence and floral characters in H. melanocarpa. As recognized previously (Burt-Utley and Utley 1987), staminate inflorescences of this species are characteristically tripinnate whereas pistillate inflorescences are bipinnate. Moreover, nodes of ataminate and often pistillate inflorescences of H. melanocarpa bear fascicles of lateral branches. Within a fascicle, the central branch is typically best developed, as determined by its greater length and more numerous flowers. While we have regularly observed multiple branches per staminate inflorescence node (5-7), pistillate nodes typically have a central, elongate branch with a shorter branch on either side. Often these shorter branches do not develop, resulting in a single lateral branch at each node. With respect to floral characters, staminate sepals range from broadly oblong to broadly ovate or ovate-triangular with rounded apex, whereas pistillate sepals are broadly triangular and acute. The most obvious floral difference between staminate and pistillate flowers is petal shape. In staminate flowers, petals are convex and suborbicular to broadly oblong at anthesis, a marked contrast to the narrowly ovate or ovate-triangular pistillatr petals. Differences similar to those observed between the sexes in H. melanocarpa have, in at least one instance, resulted in the recognition of males and females as distinct species (H. scariosa Lyman B. Smith and H. texensis S. Watson) (Burt-Utley and Utley 1987). —See Smith & Downs 1974
