Studies in the genus Riccia (Marchantiales) from southern Africa. 15. R. hirsuta and R. tomentosa , sp. nov., two distinct species previously treated as one

The description of Riccia hirsuta (Volk & Perold 1986) is emended and new illustrations of the species are provided, as the original description and illustrations were based on two distinct, but rather similar species. Examination of newly collected material of R. hirsuta, showed it to belong to subgenus Riccia, section Pilifer (Volk 1983). Section Micantes (Volk & Perold 1986) of which this was the type species, is therefore transferred to section Pilifer. R. tomentosa Volk & Perold, sp. nov., described here, is at first glance somewhat similar to R. hirsuta in its habit, hence the earlier confusion in Volk & Perold (1986). It also resembles R. hirsuta in its dorsal covering of long hairs and in the triangular scales apically split into cellular strands. R. tomentosa, however, differs from R. hirsuta in the spongy (not compact) construction of the thallus and in the spores permanently united in tetrads (not single). It belongs to subgenus Thallocarpus and is the type species of the new section Pannosae


INTRODUCTION
When R. hirsuta Volk & Perold (1986), the figures of which are referred to below as 1986, was described, it was assumed that all five specimens then listed under this species, definitely belonged here.Among these specimens, only Oliver 8040 had mature spores.Even though there were some indications that the material was not quite homogeneous, the possibility of another, rather similar species, existing in the same area seemed remote, and it was assumed that all material belonged to one species.During fieldwork by Perold in Namaqualand in September/October 1987 and August/September 1988 and by Oliver in July 1989, six new collections of densely hairy specimens were made, each one with distinctly papillose spores which on maturity remain in permanent, ± globular tetrahedral tetrads.These collections belong to a new species, R. tomentosa (see below).Fresh gatherings of/?, hirsuta, also with a dense dorsal hair covering but with single, reticulately ornamented spores were also made, thus providing more material for study.

CORRECTION OF PUBLISHED ILLUSTRATIONS
The existence of two similar-looking species, in the same area, regrettably gave rise to mistakes not only in the naming of the specimens, but also in the illustrations (Volk & Perold 1986).Specimens from both species were used for Figures 1 and 2 thick, i.e. about once to twice wider than thick; oblong, broadening towards truncate apex (Figure 2B); groove short, soon becoming flat; margins subacute; flanks sloping outwards in a short wing (Figure ID), greyish green, occasionally with some reddish pur ple flecks; ventral surface slightly rounded to plane, pale green; when dry (Figure IB), sides partly inflexed, dorsal surface grey, dusty from accumulation of sand grains trapped between hairs.
diameter; central ridges thick and high, outer ridges thinner and lower, sometimes extending partly on to wing (Figure 1986: 3C, D); proximal face with triradiate mark distinct, but poorly delineated, each facet irregularly and rarely completely reticulate (Figures 2G; 1986: 3A, B).Chromosome number n = 8 (Bornefeld in Volk & Perold 1986) (Figure 1H).R. hirsuta is extremely rare and only known from the plateau N of Leliefontein (Figure 3) (altitude ± 1 500 m above sea level), in a winter rainfall area with less than 200 mm rain per annum.It grows in association with other Riccia species, e.g.R. limbata Bisch., R. bullosa Link ex Lindenb., R. cupulifera A.V. Duthie and R. schelpei Volk & Perold, on clayey soil, at a seepage area or in seasonally damp sandy places between small shrublets and Restionaceae.R. hirsuta is distinguished from other species in sectionPilifer by the very tall, shiny dorsal cell pillars and by the triangular scales, apically split into filamentous, short, loose, cellular strands.
FIGURE 2 .-Ricciahirsuta.Morphology and anatomy, spore ornamentation.A, two young thalli; B, apex of thallus from above, densely hairy; C, apices of hair pillars; D, part of transverse section, showing bases of hairs and young antheridial neck; E, two rows of 4-sided air pores, from above, hairs partly removed; F, thallus flank with four scales, two central ones with appendages; G, proximal face of spore; H, distal face; I, side view of distal face.A, B, D, Oliver 8040 (type); C, E-I, S.M. Perold 2101.A,D, LM micrographs by Volk; B, C, E-I, SEM micrographs by Perold.Scale bars on A = 1 mm; B -F = 100 /zm; G -I = 50 /xm.
Riccia presently known, R. tomen tosa occupies a unique position as it has both primitive and derived characters.The spores of subgenus Thallocarpus which remain in tetrads, are regarded as primitive (Jovet-Ast 1987), as are also the 'loose' construc tion of the assimilation tissue with wide lacunae, and the chlorophyllose epidermis which is pierced by air pores (stomata) that are circumscribed and separated by a ring of cells.Regarded as derived characters are the hairy covering of the dorsal surface of the thallus (similar to that in the section Pilifer, subgenus Riccia) and the raised basal cells of the larger hairs.
(pp. 188 & 189).For Figures IB, H and 2A-H, Le Roux & Fourie PRE-CH4494 was used and for Figure ID, Schelpe 7784; these two specimens were collected from the same population, and are R. tomentosa; firstly, because the air pores are distant and secondly, because the spores from Schelpe 7784,