Review of the genus Xenoscapa ( Iridaceae : Crocoideae ) , including X . grandiflora , a new species from southern Namibia

The small genus Xenoscapa (Goldblatt) Goldblatt & J.C.Manning, endemic to the southern African winter rainfall region, is reviewed. The new species X. grandiflora is described from the deeply dissected southern part of the Huib Hoch Plateau in southern Namibia. It differs from the two known species in the genus in its significantly larger, pale lilac flowers. Full descriptions and accounts of all three known species are provided, with distribution maps and illustrations.


INTRODUCTION
Xenoscapa (Goldblatt) Goldblatt & J.C.Manning, one of the smallest genera in Iridaceae, currently comprises two species from the winter rainfall region of southern Namibia and southwestern South Africa.Both are small, deciduous geophytes with two or three, soft-textured, prostrate foliage leaves and unusual, single-flowered, mostly shortly branched spikes (Goldblatt & Manning 1995, 2008).The vegetative similarity between them extends to the flowers, which are long-tubed with relatively small, narrow tepals and shortly exserted, arcuate stamens.
The distinctive combination of single-flowered spikes, tubular flowers, and deeply divided style branches caused a great deal of uncertainty about the taxonomic position of the genus.The slender perianth tube and divided style branches caused the first known species, Xenoscapa fistulosa (Spreng.ex Klatt) Goldblatt & J.C.Manning, to be described in the genus Ovieda Spreng.(an illegitimate later synonym of Lapeirousia Pourr.), from which it was subsequently transferred to Lapeirousia (Baker 1877).The rounded corms with fibrous tunics are anomalous there, however, and it was accordingly moved to Anomatheca as the monotypic section Xenoscapa (Goldblatt 1972).A later morphological cladistic analysis indicated that the species was also misplaced here, combining a unique mix of mainly apomorphic character states, notably the unusual inflorescence, reduced leaf number and cylindrical capsules, containing plesiomorphic, angled seeds.As a result, Xenoscapa was recognized as an independent genus, and increased to two species with the addition of a new species from central Namaqualand, X. uliginosa Goldblatt & J.C.Manning.The precise relationships of Xenoscapa remained uncertain until recent analysis of plastid sequence data placed it as sister to the clade comprising Devia-Crocosmia-Freesia (Goldblatt et al. 2006).The four genera are currently treated as the tribe Freesieae (Goldblatt & Manning 2008).
The two known species of Xenoscapa are distinguished by small differences in perianth size and colour, height of the flowering stems in fruit, and the presence or absence of floral fragrance (Table 1).X. fistulosa is relatively widespread, occurring throughout the range of the genus, from the Huib Hoch Plateau in southern Nambia southwards along the Namaqualand escarpment and the interior mountains of the southwestern Cape, with two outlying populations along the West Coast (Goldblatt & Manning 2000a).X. uliginosa, in contrast, is a highly local endemic restricted to middle and upper elevations of the Kamiesberg, where it may co-occur with X. fistulosa (Goldblatt & Manning 1995).A recent collection from the summit of Hohenzollern Peak in the Hunsberge in southern Namibia, slightly east of the recorded range of X. fistulosa, is distinctive in its significantly larger, pale lilac flowers with relatively larger anthers, and represents a third species, described here as X. grandiflora.We take this opportunity to provide a review of the genus Xenoscapa.to Holmgren et al. 1990).The abbreviation of author names follows Brummitt & Powell (1992).
Seasonal perennials with small, globose corm, rooting from the base and axial in origin; tunics of finely reticulate fibres.Cataphylls 2 or 3, pale and membranous.Leaves 2 or 3, unifacial, prostrate, soft-textured, with definite midrib; margins with columnar epidermal cells.Stem short or long, erect, terete, often with 1-3 short branches.Inflorescence of solitary, sessile flowers terminal on axes; bracts green, leathery, inner bracts slightly shorter or more often slightly longer than outer, often notched apically.Flowers zygomorphic, tubular or salver-shaped, either cream-coloured and sweetly scented or pink with contrasting markings on lower tepals and unscented, with nectar from septal nectaries; perianth tube cylindric and elongate; tepals subequal, spreading or dorsal erect, slightly larger, and spoon-shaped.Stamens unilateral and arcuate, filaments shortly exserted.Ovary globose, sessile; style filiform, with short, deeply divided, recurved branches.Capsules oblong to cylindric, cartilaginous.Seeds strongly angled, with prominent chalazal crest, slightly wrinkled, matte, surface colliculate-rugulose. Basic chromosome number x = 11.Three species, in the southern African winter rainfall zone of southern Namibia and western South Africa.
Etymology: from the Greek, xenos, for strange and scapa, for flowering stem, because of the inflorescence, unusual for subfamily Crocoideae in bearing solitary flowers on the main and lateral branches instead of spikes of multiple flowers.
Distribution and ecology: known only from the type collection, made on the summit of Hohenzollern Peak at the southern end of the Hunsberge in southern Namibia (Figure 2) on 1 July 2007 by horticulturist Ernst van Jaarsveld.The plants were tightly wedged in crevices in the shelter of rock outcrops immediately below the eastern edge of the summit plateau, and were just past flowering.Corms that were collected then have subsequently flowered in cultivation.Vegetatively, these plants match photographs of wild plants taken at the time and there is no reason to expect that the dimensions derived from the cultivated specimens will differ in any meaningful way from specimens in the wild.The Hunsberge, in the deeply dissected southern part of the Huib Hoch Plateau, are a recognized site of ecological importance in Namibia, known for a high level of endemism among vertebrates (Barnard et al. 1998).
Diagnosis and relationships: Xenoscapa grandiflora is distinguished by its large, unscented, pale lilac flowers marked with purple chevrons on the lower tepals, a perianth tube 33-35 mm long and the tepals 12-14 × 4.0-5.5 mm.
Xenoscapa grandiflora is most likely to be confused with X. uliginosa from the Kamiesberg, both of which have relatively larger, unscented, generally pink flowers with darker chevrons on the lower tepals but the latter has bright pink or purple flowers with a shorter perianth tube, 22-28 mm long, and smaller tepals, 6-7 mm long, with the dorsal tepal typically suberect or spreading to expose the stamens and style rather than remaining erect after anthesis (Figure 1E).The common and widespread X. fistulosa has smaller flowers with uniformly white or cream-coloured (rarely pale pink) tepals (although the tube is usually flushed maroon) and a distinct and noticeable floral fragrance (described as sweetly clove-like).
Both Xenoscapa fistulosa and X. grandiflora are self-fertile and autogamous, with all flowers setting full capsules of seed that appear well formed (reproductive biology is unknown in X. uliginosa).The unscented, lilac flowers with elongate perianth tube and dark purple markings on the lower tepals of X. grandiflora are consistent with pollination by long-proboscid flies, the pollination system in X. uliginosa (Manning & Goldblatt 1996;Goldblatt & Manning 2000b).Distribution and ecology: restricted to the Kamiesberg in central Namaqualand, and known originally only from the Sneeuberg but recently collected in the Langkloof east of Stalberg, at the foot of Rooiberg (Figure 2).Xenoscapa uliginosa has a specialized habit along the margins of seasonal seeps and in rock flushes.During the growing season the roots are constantly irrigated by water percolating through the mossy sward in which the corms are anchored.
Diagnosis and relationships: Xenoscapa uliginosa is recognized by its moderately large, dark pink or purple, unscented flowers marked with purple chevrons on the lower tepals, perianth tube 22-28 mm long, and tepals 6-7 × 2-3 mm.Plants from the Sneeuberg have the dorsal tepal ± suberect to expose the anthers and style but a recent collection from the Langkoof on the southern flank of the Rooiberg massif (Goldblatt & Porter 13575), representing the second known station for the species, has the dorsal tepal erect over the stamens and style, and the length of the perianth tube at the lower end of the range recorded for the species.In other respects, however, including the short, oblong capsules, the Rooiberg plants match those from the type locality and there is at present no reason to suspect that they are not conspecific.
The species might be confused with Xenoscapa grandiflora from southern Namibia but that species has larger, pale lilac flowers with a much longer perianth tube, 33-35 mm long, and the dorsal tepal 12-14 mm long.Flowering in X. uliginosa is also generally later, in September and October (rarely into November) rather than in mid-winter.
Distribution and ecology: widely distributed along the near interior of the southern African Atlantic coast and the western Karoo, Xenoscapa fistulosa extends from Aurusberg and the southern edge of the Huib Hoch Plateau in southern Namibia through the higher-lying parts of the Richtersveld and Namaqualand into Western Cape, where it occurs in the northern Cedarberg and inland onto the Roggeveld Escarpment, thence southwards into the Worcester Valley as far east as Montagu and thence to Laingsburg and the northern foothills of the Klein Swartberg, with two isolated stations along the coast, one at Vredenburg and the other on the lower slopes of Lion's Head on the Cape Peninsula (Figure 2).The species is mostly restricted to shale or gneiss/granite substrates, rarely on other rock types in the Richtersveld and southern Namibia, from near sea level to almost 1 300 m.It does not occur on sandstone-derived soils of the Cape System and is thus virtually absent from the southwestern Cape mountain systems-the two coastal stations in the southwestern Cape are on granite outcrops.
Plants are invariably restricted to cool, seasonally moist or wet and largely shaded situations in the lee of rocks or boulders, with the corms often anchored in moss pads.The flowering season is substantially lengthened in years of favourable rainfall by the development of a secondary inflorescence from the upper leaf axil.This has not been observed in the other two species.
The pale, mostly white or cream-coloured flowers of Xenoscapa fistulosa with their sweet-spicy fragrance suggest that the species is adapted to moth pollination.It co-occurs with long-proboscid fly-pollinated X. uliginosa in the Kamiesberg (Bean & Trinder-Smith 2642& 2634 respectively), and hybrids between the two (Goldblatt 9244A MO) are known (Goldblatt & Manning 1995).
Diagnosis and relationhips: Xenoscapa fistulosa is recognized by relatively long-tubed, white or creamcoloured (rarely pale pink) flowers with a strong sweetspicy fragrance.The slender perianth tube is mostly 18-25 mm long, exceptionally 30-33 mm long in plants from Pakhuis Pass and the northern Cedarberg (Leipoldt s.n., Goldblatt 544), and only 1.0-1.5 mm in diameter at the mouth.The tepals are mostly smaller and narrower, 4-6(-7) × 1-3 mm, than in pink-flowered X. grandiflora and X. uliginosa (Table 1).Most collectors remark on the strong floral fragrance, which immediately distinguishes the species from its unscented congeners.
Although the species is typically white-flowered, populations from the Richtersveld and southern Namibia often have pale pink flowers [see Williamson (2000): 127 Xenoscapa fastuosa (sic.) for illustration].The smallestflowered species in the genus, X. fistulosa may grow much taller than the other species, the stem reaching up to 180 mm long, with the lateral branches up to 30 mm long.The capsules are similarly often significantly longer, up to 18 mm long and strongly cylindric.The two outlying coastal populations, from Witteklip at Vredenburg and Lion's Head on the Cape Peninsula, although well separated geographically from the main range of the species, do not evidently differ morphologically from inland populations.