Comparative stem anatomy and systematics of Eriosyce sensu lato (Cactaceae)

Abstract

The genus Eriosyce as circumscribed by Kattermann (Succulent Plant Research 1: 1-176, 1994) comprises six subsections with 33 species and 38 heterotypic infraspecific taxa and is restricted in distribution to Chile and NW Argentina. A total of 19 anatomical and gross morphological characters were studied from stem material of 27 taxa of Eriosyce and six outgroup taxa from the genera Austrocactus, Copiapoa, Corryocactus, Eulychnia and Neowerdermannia (all from the tribe Notocacteae of subfamily Cactoideae). Comparisons between field-collected and glasshouse-cultivated plant material, as well as comparisons between samples from different positions on the stem, allowed an assessment of the variability of various characters. A detailed cladistic investigation with different character composition and character coding was conducted to check for combinations of characters that support a number of different clades. Eriosyce subsect. Chileosyce (including E. napina and E. odieri, but excluding E. laui) and E. subsect. Neoporteria are very well characterized by a number of the attributes investigated, such as a papillate or completely fiat epidermal relief, a very soft and strongly mucilaginous cortex, or a tuberculate stem with the podaria arranged in helical lines. The usefulness of the anatomical and morphological data was examined further by a cladistic analysis of a subgroup of 21 taxa supplemented with data on flowers, fruits and seeds (data from published sources). The present circumscription of Eriosyce (including Horridocactus, Neoporteria, and Thelocephala) is not seriously questioned by these cladistic analyses, with the possible exception of Islaya. The position of E. laui remains unresolved.