New Species of Aristea Section Racemosae (Iridaceae) from the Cape Flora, South Africa

Abstract

Aristeafimbriata, A. inaequalis, and A. rupicola are new to this genus of some 52 species of sub-Saharan Africa and Madagascar. The new species all occur in the western part of the southern African winter-rainfall climatic zone and are highly local endemics, two of them known only from single extended populations. All three species have threewinged capsules, a specialized condition that defines subgenus Aristea, a taxon virtually restricted to the southern African winter-rainfall zone. In addition the new species have pollen grains with apertures confined to one face of the grain, either monosulcate or trichotomosulcate, and have specialized, undivided styles that define section Racemosae, one of two sections of subgenus Aristea. Observations on the pollination biology of A. inaequalis show that it is probably pollinated by female Anthophora diversipes (Anthophoridae) bees, which forage for pollen on the flowers of this species. This pollination strategy conforms to that of other blueflowered species of the genus, that is, they have flowers adapted for pollination by various species of female bees foraging for pollen. A revised key to section Racemosae is presented, which includes entries for apparently undescribed taxa that require further investigation. Section Racemosae is one of two sections of the exclusively southern African subgenus Aristea of the sub-Saharan African and Malagasy genus Aristea, which comprises some 52 species (Weimarck, 1940; Goldblatt & Manning, 1997; Goldblatt & Le Thomas, 1997). Both section Aristea, with 6 species, and section Racemosae, with an estimated 14 including the 3 new species described here, are largely restricted to the southern African winter-rainfall zone in the south and west of the subcontinent. They also occur almost exclusively on the nutrient-poor, well-drained, rocky sandstone-derived soils that characterize a large part of the winter-rainfall zone. Here we describe three new species of section Racemosae, all narrow endemics of the western half of the winter-rainfall zone. Two of these, Aristeafimbriata and A. rupicola, are comparatively recent discoveries, but A. inaequalis has been known at least since 1911, when it was collected by E. P. Phillips on the Gifberg in northern Western Cape Province. That species has, however, often been confused in herbaria with A. monticola Goldblatt, also called A. caerulea Thunberg, an illegitimate superfluous name (Goldblatt & Barnard, 1970). No specimens ofA. inaequalis were, however, cited under any species of section Racemosae by Weimarck (1940) in the only complete, modemrn account ofArist a, a treatment now seriously out-of-date. All three new species described here have the plesiomorphic pollen grains with a single aperture confined to one surface of the grain and derived, undivid d style branches that characterize section Racemosae (Goldblatt & Le Thomas, 1997), as well as broadly winged capsules with two to four radially compressed seeds per locule that define subgenus Aristea. Aristeafimbriata is distinctive in its low stature, inflorescence with the spathes and bracts fringed and brown-tipped, and, moreover, stands out palynologically in the section in having pollen grains with a trichotomosulcate aperture (Le Thomas et al., 1996; Goldblatt & Le Thomas, 1997). Other species of the section have pollen grains with a conventional elliptic aperture except for one evidently aberrant population of A. zeyheri Baker, which has zonasulculate grains. Plants from other populations have typical monosulcate pollen grains (Goldblatt & Manning, 1997). Aristea inaequalis and A. rupicola are lithophytes and only grow in rock crevices in sandstone outcrops, a habitat that is unusual in the genus. 1. Aristea inaequalis Goldblatt & J. C. Manning, sp. nov. TYPE: South Africa. Western Cape: rocky sandstone plateau at the top of Gifberg, 3 Oct. 1996, Goldblatt & Manning 10561 (holotype, NBG; isotypes, K, MO). Figures 1, 2. Plantae ca. 100-150 cm altae caespitosae, foliis distiNovoN 7: 357-365. 1997. This content downloaded from 157.55.39.177 on Sat, 19 Nov 2016 04:34:40 UTC All use subject to http://about.jstor.org/terms