Caesia sabulosa (Hemerocallidaceae), a new species from the Greater Cape Region of South Africa

The new species Caesia sabulosa Boatwr. and J.C.Manning from deep sands along the West Coast of South Africa and sandy flats in the Cederberg and Bokkeveld Escarpment is described. It is distinguished by its extensively branched rhizome resulting in a robust, clump-forming habit, and unique ‘palisade’ root system of closely packed, hard, vertical roots; mostly larger flowers; erect fruiting pedicels; and details of the seed testa sculpturing. © 2010 SAAB. Published by Elsevier B.V. All rights reserved.


Introduction
Caesia R.Br. comprises ± 11 species of tufted, grass-like plants with delicate, short-lived, white, blue or purple flowers in which the perianth twists spirally when they fade (Henderson, 1987;Obermeyer, 1973). Some of the species have very colourful, horizontally barred filaments with alternate yellow, white and purple transverse bands in various patterns (Fig. 1). The main centre of diversity for the genus is in Australia, where eight species are found, seven of them endemic (Henderson, 1987). One species occurs in Madagascar and an additional two species are found in South Africa, predominantly in the Western Cape (Obermeyer, 1973). The two South African species were last studied by Obermeyer (1973) who transferred Nanolirion capense (H.Bolus) Benth. and Hook. to the genus Caesia [as Caesia capensis (H.Bolus.) Oberm.] and also placed several species into the synonymy of Caesia contorta (L.f.) Dur. and Schinz, based on studies of herbarium specimens, concluding that these represent different forms of one variable species. However, further field studies are crucial to understanding the variation in the C. contorta complex to ascertain whether it indeed represents a single species.
The familial placement of the genus has been somewhat volatile with various authors assigning it to different families, i.e. Asphodelaceae subfamily Anthericoideae (Dahlgren and Clifford, 1982), Anthericaceae (Dahlgren et al., 1985), Phormiaceae (Chase et al., 1996), Johnsoniaceae (Clifford and Conran, 1998) and Hemerocallidaceae Fay et al., 2000). Recent molecular data place Caesia in the "hemerocallid clade", which includes members of the families Hemerocallidaceae, Johnsoniaceae and Phormiaceae and which is sister to Asphodelaceae and Xanthorrhoeaceae (Devey et al., 2006). The most recent classification system of the Angiosperm Phylogeny Group (APG III, 2009), proposes a greatly expanded concept of the previously monotypic family Xanthorrhoeaceae to include both the Asphodelaceae and the "hemerocallid clade" but we follow the more conservative classification of APG II (2003), which retains Hemerocallidaceae in an expanded circumscription to include Johnsoniaceae and Phormiaceae rather than including it within a broad concept of Xanthorrhoeaceae.
Here we describe a new species of Caesia that was previously recognized informally as Caesia sp. 1 in Goldblatt and Manning (2000), raising to the 12 number of species in the genus. This work forms part of a broader systematic and taxonomic study of the South African species and their relationship to their Australian counterparts, including field work to unravel the variation within the species and their circumscription.

Materials and methods
Morphological data on the new species were gained through field studies, as well as examination of herbarium material from BOL, K, NBG and PRE (abbreviations according to Holmgren et al., 1990). Seed surface sculpturing of the three South African Caesia species was examined with an LEO S440 fully analytical Scanning Electron Microscope (SEM) after being coated with gold. This was done at the Electron Microscope Unit, University of Cape Town. Voucher information of the species studied is listed in Table 1. Drawings were done using a stereoscope (WILD M4A) with a camera lucida attachment.

Species
Locality

Diagnostic characters
Caesia sabulosa resembles the widespread C. contorta in its long, distichous, conduplicate leaves, divaricately branched panicle, and deciduous, tripartite, turbinate capsules in which mostly one or sometimes two locules ripen, but the two species differ considerably in habit and root structure, flower colour in some forms, and details of the fruit and seeds. The rhizome in C. sabulosa is extensively branched, with the result that the species develops a distinctive, clumped growth habit (Fig. 1d), with the larger clumps reaching up to 2 m in diameter. The species grows in deep, sometimes coastal sands often in association with restioid taxa, and the root system is well-adapted to the loose substrate, producing numerous hard, tapering roots that are closely packed along the rhizomes and that grow vertically downwards into the soil, forming a dense, palisade-like structure serving to anchor the plants securely. The pink to deep blue flowers are borne in stiffly erect panicles that project above the foliage (Fig. 1d), and anthesis takes place during the morning, with the flowers fading during the afternoon. The fruiting pedicels remain erect, and the capsules are shed as soon as they ripen, collecting around the base of the plant. The rhizome in C. contorta is far less extensive, with the plants typically solitary (Fig. 1e), and the roots are wiry and spreading. The pale blue to purple flowers are borne in sprawling or trailing panicles that develop characteristic tufts of leaves from the lower leaf axils (Fig. 1e), and anthesis takes place only in the early afternoon, with the flowers fading in the early evening. The fruiting pedicels are recurved, with the capsules nodding.
The remaining South African species, C. capensis is a small caespitose and mat-forming plant less than 80 mm high with subumbellate inflorescences or solitary flowers with smooth filaments.
Surface sculpturing of the seeds is taxonomically informative in the three South African species and has also been used as a key character in the Australian species (Henderson, 1987;Fig. 3). The seeds of the three South African species are black with fleshy white strophioles, reniform in C. capensis and C. contorta but globose in C. sabulosa. The fleshy strophioles (generally referred to as elaiosomes) attract ants which carry the seeds to their nest thus distributing the seeds away from the mother plant and providing protection from predation or unfavourable conditions (myrmecochory; Lengyel et al., 2010). Surface sculpturing in all three species is striate-verrucose, with a mix of large and small tubercles. In C. sabulosa and C. capensis the large tubercles are surrounded by valleys of much smaller tubercles, with the larger tubercles arranged in irregular clusters in C. capensis and in short, narrow rows in C. sabulosa (Fig. 3a-d). In C. contorta the tubercles in the valleys are diagnostically only somewhat smaller than the large tubercles, which are distributed randomly (Fig. 3e-f). In C. capensis and C. contorta the tubercles are conical, terminating in a small conspicuous point, while in C. sabulosa the tubercles are spherical and smooth.

Distribution and habitat
Caesia sabulosa grows in deep sands along the Western Cape coast, from Silverstroomstrand to Redelinghuys (in Atlantis Sand Fynbos, Hopefield Sand Fynbos and Leipoldville Sand Fynbos plant communities; Rebelo et al., 2006) and as far north as Kotzesrus in Namaqualand (in Namaqualand Strandveld; Rebelo et al., 2006), and inland along the Cederberg and Bokkebeld Mountains (in Cederberg Sandstone Fynbos and Bokkeveld Sandstone Fynbos;Rebelo et al., 2006;Fig. 4). A similar distribution pattern is evident in another psammophilous species, Babiana ringens (L.) Ker Gawl. (Goldblatt and Manning, 2007). Typical populations of C. sabulosa along the West Coast south of Redelinghuys have distinctive, pink flowers but populations from the Bokkeveld Escarpment and Cederberg have a blue or purple perianth. They show the characteristic rather rigid panicles with large flowers and erect capsules of the coastal forms and we include them here pending further field work to understand this floral variation.