Studies in the genus Riccia ( Marchantiales ) from southern Africa . 18 . New species in section Pilifer from the NW Cape : R . furfuracea

Another three new species of Riccia in section Pilifer Volk are described from Namaqualand, namely R. furfuracea, R vitrea and R. namaquensis. There are certainly more undescribed species present in that region, but species from there are often very difficult to distinguish: almost all have hyaline scales, the free-standing dorsal cell pillars need to be examined in living plants and the spore ornamentation is quite variable.


INTRODUCTION
Namaqualand lies in the north-western and western Cape Province; it comprises four regions: the Richtersveld, the Sandveld, the Knersvlakte and the Namaqualand Klipkoppe (domed, granite hills) which are geographically and floristically quite distinct.The region is + 100 -2(K) m above sea level, with its mountainous areas at an elevation of less than 2 (KK) m.Namaqualand is arid with sporadic sparse winter rain, 100 -200 mm p.a., yet it is renowned for its magnificent display of spring flowers.
In this area species of section Pilifer are common, in contrast with the summer rainfall parts of southern Africa, where they are much scarcer and belong to different species.Mosses frequently growing in association with Riccia spp. in this region are Barbula crinita Schultz, Three new species in section Pilifer from Namaqualand are described in this paper: R. furfuracea, R. vitrea and R. namaquensis.It is quite certain that there are more species present, some probably with a restricted distribution, but it is generally very difficult to distinguish between them vegetatively, as differences are often subtle.Nearly all have rounded hyaline scales and the fragile, somewhat variable, dorsal cell pillars, which constitute a most important character, need to be examined in living plants.Under different conditions of growth and in cultivation, these Riccia species display the same plasticity of the gametophyte that makes the taxonomy of much of the genus so difficult.Moreover, two or more species commonly grow together in mixed stands, which can be confusing, especially if the sporangia have disintegrated and the spores are scattered.
Spores from all sporulating material of species in section Pilifer held at BOL and PRE have been studied by SFM and LM but, with some exceptions, the spore ornamenta tion shows a spectrum of variation which unfortunately often makes it a less reliable and useful distinguishing character in this section.It would appear that continued observation over several seasons of marked populations in the field, and the use of a fully equipped mobile laboratory may be the only means toward clearly defining the characters and limits of more species, but the long travelling distances involved make it rather unpractical.To isolate species, some other reliable vegetative characters are needed, such as isozymes, which Dewey (1988) separated by starch gel electrophoresis and found to be species specific, but once again, living plants are required.Regrettably, it seems therefore that many collections, especially the older ones, of species in section Pilifer are unidentifiable, at least for the present.
The specific epithet, furfuracea, is derived from the Latin furfuraceus meaning scurfy, and refers to the roughened dorsal surface of the dry thallus.This species is recognized by, and distinguished from other Riccia species in section Pilifer, that have rather low dorsal pillars with ± bulging cells, such as R. concava Bisch.ex Krauss (Perold 1989c), R. elongata Perold (1990b), R. trachyglos sum Perold (1990b) and R. pulveracea Perold (1990c), by the mammillose top cells, closely packed together, neither arranged in rows nor uniform in size, by large apical scales and by coarsely reticulate spores with a central cross on the distal face and low-walled, poorly defined areolae on the proximal face.
It often grows together with other Riccia species on soil at the margins of granitic rock outcrops, near seepages or on stream banks.It is only known from the north western and south-western Cape (Figure 4). 2. R iccia vitrea Perold, sp.nov.
R. vitrea has been so named because of the similarity of the tall dorsal cell pillars in full grown, living plants, to glass (Latin: vitrum), or rather, slivers of shattered glass.It can be recognized by the large billowing, hyaline scales, sometimes turning a pale cream colour while remaining transparent, and by the tall dorsal cell pillars, similar to those in R. villosa Steph.and R. simii Perold (1990a) (= R. albomarginata auct.non Bisch.) but not so 'fine', hardly tapering and often interlocking.The spores are variable in size and in ornamentation, especially on the distal face which is completely to incompletely reticulate.Spores from some specimens, Perold 1423, 1424 and 1475, were repeatedly examined and photographed.A number of specimens placed here were not fertile, however; others had few sporangia, whereas in Perold 1423, they were present in abundance, but seemingly from the previous season, as many had disintegrated.Gemmae were found in the type specimen, Perold 1475.R. vitrea is so far known from only a few localities in Namaqualand (Figure 4), where it grows in crowded stands at seepages, on generally rather coarsely grained soil der ived from exfoliating granitic rock, together with R. bul losa Link ex Lindenb., R. albomarginata Bisch.ex Krauss, R. schelpei Volk & Perold (1986a), R. nama quensis Perold (1990b) and R. furfuracea Perold (1990b).
FIGURE 6. -Riccia vitrea.Morphology and anatomy.A, thalli in cultivation; B, branches seen from above; C, branches seen partly from the side; D, apical scales and dorsal cell pillars arched over groove; E, arched dorsal cell pillars; F, erect dorsal cell pillars.A -F , S.M. Perold 2149.A, by A. Romanowski; B -E , SEM micrographs.Scale bar on A -D = 1 mm; E, F = 50 /xm.

FIGURE 9 .
FIGURE 9.-Riccia namaquensis.Morphology and anatomy.A, thalli in cultivation; B, branches from above; C, scales at apex, seen from the side; D, groove and scales at apex; E, dorsal pillars from above; F, dorsal pillars seen partly from the side.A -F , S.M. Perold 2136.A, by A. Romanowski; B -F , SEM micrographs.Scale bar on A -D = 1 mm; E, F = 50 /zm.