Maihueniopsis is one of several genera that have been split from Opuntia because of research by Steven Dickie and Robert Wallace (2001), James Iliff (2001), and Wolfgang Stuppy (2001). The South American members of the subfamily Opuntioideae have been, and continue to be, a challenge to the cactus taxonomist. Several smaller genera, representing separate lineages, explain the relationships of the cacti better than would a single large genus Opuntia, which is polyphyletic.

Maihueniopsis (type, M. molfinoi = M. glomerata) was described in 1925 by Carlos Spegazzini, the name derived from the Greek opsis, appearance, thus Maihuenia-like. Research has shown, however, that Maihueniopsis and Maihuenia are not closely related. Puna, described by Roberto Kiesling in 1982, has been included in Maihueniopsis but with uncertainty. David Ferguson and Kiesling (1997) characterize Puna as geophytic, with large tuberous roots from which arise soft stems arranged in a series of densely stacked segments. They agree that the relationship of Puna to other op-untioids is uncertain but add that its fruits and seeds are similar to those of Maihueniopsis. DNA sequencing by Dickie and Wallace and seed studies by Stuppy do not indicate that Puna is distinct; rather, it appears to be nested within Maihueniopsis.

Thus defined, Maihueniopsis comprises 18 species, not all well understood and further clarification remaining necessary. The genus is characterized as having a specialized growth habit in which the plants usually form compact cushions with inconspicuously segmented stems, tuberous roots, and areoles located in depressions. The seeds have a unique funicular envelope that is soft and woolly.

Maihueniopsis Spegazzini 1925, emended by F. Ritter 1980 Pseudotephrocactus Fric & Schelle 1932-1933, not validly published Puna R. Kiesling 1982

Subfamily Opuntioideae. Plants not treelike, densely branched, cushion forming, with stems indistinctly segmented. Roots tuberous. Stem segments characteristically ovoid, usually round in cross section, not dimorphic, with determinate growth, 2-20 cm (0.8-7.9 in) long. Leaves small, falling away early. Areoles located In depressions, bearing hairs, glochids, and usually spines. Spines often flattened. Flowers yellow; pericarpels with fewerthan 30 areoles. Fruits fleshy, indehiscent, greenish or yellowish; if spiny, then with longer spines above, or the spines near or on the rim only. Seeds not markedly tapered, funicular envelope soft and woolly, 6 mm (0.2 in) long. Distribution: Peru, Bolivia, Chile, and Argentina.

400 Maihueniopsis archiconoidea

Maihueniopsis archiconoidea F. Ritter 1980 Opuntia archiconoidea (F. Ritter) D. R. Hunt 1997

Plants small, forming cushions to 20 cm (7.9 in) wide. Roots deep. Stem segments globose to conical, to 1.7 cm (0.7 in) long, without tubercles. Areoles about 30 and extending to base of the segment, close set, very small and crowded api-cally, the upper half with spines. Glochids very prominent, bushy, especially on lower areoles. Central spine one, sometimes absent, straight, flat, broad based, tapering, bent away, white with brown tip, to 15 mm (0.6 in) long. Radial spines 3-5, unequal, irregularly curved or pointing downward, the smaller ones lying next to the surface. Flowers not known. Distribution: Atacama, Chile.

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