Chlorophytum boomense (Agavaceae) is a synonym of C. namaquense from southern Namibia and the Northern Cape, South Africa

Chlorophytum Ker Gawl. (Agavaceae) (sensu APGII 2003; Manning & Goldblatt 2012) includes 150–200 species of rhizomatous perennials distributed widely through the Old World tropics and subtropics, with its centre of diversity in Africa (Conran 1998; Manning 2017). The genus is well represented in southern Africa, with 40 species currently recorded from the subcontinent, twelve of which are endemic to the winter-rainfall parts of the Greater Cape Floristic Region (Manning & Goldblatt 2012; Snijman 2013; Kativu & Bjorå 2016; Manning 2017).


Introduction
Chlorophytum Ker Gawl. (Agavaceae) (sensu APGII 2003; Manning & Goldblatt 2012) includes 150-200 species of rhizomatous perennials distributed widely through the Old World tropics and subtropics, with its centre of diversity in Africa (Conran 1998;Manning 2017). The genus is well represented in southern Africa, with 40 species currently recorded from the subcontinent, twelve of which are endemic to the winter-rainfall parts of the Greater Cape Floristic Region (Manning & Goldblatt 2012;Snijman 2013;Kativu & Bjorå 2016;Manning 2017).
The southern African species were last revised some years ago by Obermeyer (1962) [see Archer and Kativu (2001) for nomenclatural corrections], but the Namibian species were more recently treated by Kativu et al. (2012). Since these publications, two additional species have been described from South Africa (Van Jaarsveld 2014; Manning 2017) and another from southern Namibia (Kativu & Bjorå 2016). The latter, C. boomense Kativu, was described from a single population from Ai-Ais Hotsprings Game Park just east of Rosh Pinah in southern Namibia. We are unable to distinguish it from C. namaquense Schltr. ex Poelln. from the Northern Cape, South Africa and southern Namibia, and formally synonymise it here.

Materials and Methods
All relevant material was examined in BOL, NBG, PRE and SAM (abbreviations following Thiers (2016)), the herbaria containing significant holdings of southern African flora. Author names are abbreviated according to the International Plant Names Index (https://www.ipni.org).

Taxonomy
Chlorophytum boomense is known from a single population along the Boom River near its confluence with the Orange River ± 30 km east of Rosh Pinah Chlorophytum boomense (Agavaceae) is a synonym of C. namaquense from southern Namibia and the Northern Cape, South Africa in southern Namibia. It was recognised as new through comparison with other species recorded from central and southern Africa, and was diagnosed against the tropical African C. subpetiolatum (Baker) Kativu on the basis of their similar roots, tapering to the tips, but is otherwise morphologically different from that taxon, and the two are evidently only distantly related (Kativu & Bjorå 2016). Chlorophytum boomense is otherwise unremarkable among the southern African members of the genus with pedicels articulated at or below the middle in having glabrous, subdistichous, linear to narrowly lanceolate leaves 8-12 mm wide, and a simple, racemose inflorescence of moderately large flowers with sparsely papillate filaments.
Chlorophytum namaquense, which was described from plants from Springbok in northern Namaqualand, was considered for a long time to be a relatively rare endemic from the immediate area (Obermeyer 1962) but is now known to occur more widely, ranging from Rosh Pinah in southern Namibia through the Richtersveld as far as Soebatsfontein in central Namaqualand, South Africa (Snijman 2013). It is diagnosed by its slender roots, elongated rosette of glabrous, lanceolate leaves to 25 mm wide with unthickened, sparsely setulose margins, and ± simple raceme of moderately large flowers with scabrid filaments, and pedicels articulated near the middle (Obermeyer 1962). Although the roots were described as slender, Obermeyer (1962) suggested that they were probably soft and spongy when young, and this is borne out in more recent collections, which have slender, tapering roots indistinguishable from C. boomense. The similarity between these two species, as well the occurrence of C. namaquense in Namibia, was overlooked by Kativu and Bjorå (2016).
A summary of taxonomically useful features in the two species (Table 1) fails to reveal any significant differences between them and we accordingly reduce C. boomense to synonymy.