Maihueniopsis

Abstract: Summary. On the basis of seed morphological and anatomical characters it is shown that the recently described third species of the genus Puna, P bonnieae, from Argentina is referable to the genus Tephrocactus. The necessary new combination is made and the conservation status of the species is assessed. During morphological and anatomical examination of the seeds of Opuntioideae (Stuppy, in press) it was found that the recently described Puna bonnieae D. J. Ferguson & R. Kiesling from the province of Catamarca, Argentina, actually belongs to the genus Tephrocactus. In fact, the original publication (Ferguson & Kiesling 1997) mentions that the plant was first taken for a Tephrocactus seedling. Morphologically, Puna bonnieae is very reminiscent of the sympatric Tephrocactus geometricus (A. Cast.) Backeb., but shows stronger adaptations to its extreme desert habitat (e.g. dwarf growth, geophytic habit). The illustrations and descriptions of the seeds in the original publication show that the species has seeds typical of Tephrocactus, and this was confirmed by morphological and anatomical investigation of seeds of the type specimen of Puna bonnieae (Fig. 1A). As will be explained in more detail and a broader context in a future article (Stuppy, in press), the seeds of the genus Tephrocactus have a unique and highly specialised structure. The funicular envelope (i.e., the outer coat of the seed originating from the funiculus) is generally glabrous, with an inner sclerenchymatous part and an outer, aerenchymatous part composed of large, radially extended, thin-walled cells with extremely wide, air-filled lumina. The embryo is hook-shaped. This peculiar and highly specialised structure of the funicular envelope clearly distinguishes the genus Tephrocactus from all other genera of Opuntioideae. Seeds of 'true' Puna, e.g. Puna clavarioides (Pfeiff.) R. Kiesling (Fig. 1B) and R subterranea (R. E. Fr.) R. Kiesling, although superficially resembling those of Tephrocactus in their texture that is soft to the touch, are very distinct in both morphology and anatomy. The sometimes apparently smooth surface of the funicular envelope is made up of thick strands of compressed unicellular trichomes formed by the cells of the outer epidermis. The tissue below the outer epidermis is uniformly composed of longitudinally elongated, thick-walled fibrous cells. The embryo is ring shaped. In fact, as will be shown in a later paper (Stuppy, in press), Puna clavarioides and R subterranea entirely agree with the genus Maihueniopsis in their seed characters, evidence upon which Anderson (1999) based the inclusion of the entire genus in Maihueniopsis.