Studies in the genus Riccia ( Marchantiales ) from southern Africa . 6 . R . hirsuta , a new species , in a new section

Riccia hirsuta Volk & Perold, sp. nov., the type species of a new section, Micantes Volk & Perold, subgenus Spongodes (Nees) Volk is described. It is characterized by tall, dorsal, hair-like, multi-cellular outgrowths from an epidermis with distant air-pores, leading to polyhedral air-chambers below, and is the only species in this subgenus with these outgrowths. The ventral scales are triangular, apically splitting into long, hair-like appendages. This species is endemic to the north-west and central Cape Province.

Thallus dorsally densely covered with multicellular, hair-like, hyaline, shiny (hence the name) pil lars.In the subgenus Spongodes no other section has these tall dorsal hairs.
Thallus monoicous (?), perennial, scattered or in incomplete rosettes, dorsally furry, whitish along margins, greenish grey over centre: medium-sized to large (Figure 1 A, B); simple or bifurcate, lobes up to 15 mm long, 2,0-4,0 (-5,0) mm broad, 1,5-2,0 mm thick, i.e. about two to three times broader than thick; oblong, obcordate when young (Figure IB), broadening towards rounded to truncate, emarginate apex; groove short, obscured by thick pelt of shiny hairs, dorsal surface soon becoming flat; mar gins subacute to slightly tumid; flanks steep to slop ing outwards in a short wing (Figure 1CP C2, C3), greyish green, occasionally with some reddish purple flecks; ventral surface slightly rounded to plane, pale green; when dry, sides partly inflexed, dorsal surface grey, dusty from accumulation of sand grains trap ped between collapsed hairs.Anatomy: dorsal cov ering of loose, hyaline, straight to bent, hair-like cell pillars (Figure 2A, B), up to 1 500 |nm long, occupy ing up to nearly 4 the thickness of frond (Figures lCj, C2, C3, 2C), consisting of one to seven thinwalled cells (Figures ID, 2D), 50-200 x 35-120 jam, tapering to apex (Table 1), distances separating bases of hairs ± 15-120 \im\ epidermis between hairs consisting of flat to slightly bulging, polvgonal cells (Figures 2G.H  parts of thallus, on transverse section (Figure 1C3).a central lenticular core is seen, where the storage cells are densely filled with fatty oil or starch, the surrounding layers of cells partially empty; rhizoids arising from ventral epidermis and base of scales, hyaline, smooth and tuberculate mixed, up to 25 [im wide.Scales large, shaggy, partly extending above margin of thallus, overlapping apicallv, triangular (Figure IE,,E3,), about 650 [im wide at base and up to 1 500 j.un high, hyaline, occasionally with reddish purple cells at base; cells at base small (Figure 1 E x), larger in body of scale and about 150 x 50 |im.ob long-hexagonal, marginal row of cells long-rectangu lar, cell walls thin, straight, toward apex cells elon gated to ± 190 |im and split up into several loose strands of about four cells (Figure 1FL ), variously bending and twisting . F3,F4).Antheridia with tall hyaline ostioles, irregularly distributed, hid den by dorsal pillars.Archegonia with purple necks.Sporangia arranged across width of thallus, up to 700 |im wide, overlying epidermis tinged with purple, containing about 650 spores.Spores triangular-globular, polar, deep dull brown to nearly black, semi transparent to opaque, (95-) 115-125 (-130) |im in diameter, with wing about 10 |im wide (Figure 3F), slightly undulating, crenulate to somewhat eroded, at angles with a pore or notched (Figure 1G, 3E); distal face reticulate, with 3-5 (-6) large central areolae, 25-38 (im wide, completely or incompletely subdivided into smaller areolae, about 12,5 (im wide, often with a papilla in the middle (Figure 3C, D), occasionally areolae equally wide and then 8-10 across diameter; central ridges thick and high, outer ridges thinner and lower, sometimes extending part ly onto wing; proximal face with triradiate mark dis tinct, but poorly delineated, each facet irregularly and rarely completely reticulated (Figure 3A, B).
R. hirsuta is endemic to.and rare in the north western Cape Province (Figure 4).It grows on sandy, acid soil and may be associated with other Riccia species, e.g.R. parvo-areolata Volk & Perold.R. bullosa Link.R. schelpei Volk & Perold.R. cupulifera A. V. Duthie.and sometimes with small shrublets such as Ruschia robusta L. Bol., and members of the Restionaceae.
The tall dorsal hair-like cell pillars have not pre viously been found in any species of the subgenus Spongodes (Nees.pro sectio) Volk (Ricciella auct., non A. Braun) (Volk 1983).They form an interest ing parallel development to the pillars in the section Pilifer Volk (1983).subgenus Riccia.where, how ever.all the columns of the assimilation tissue con tinue into loose hyaline pillars and the air-pores are formed by small interstices between rounded, densely packed, hyaline cells.R. hirsuta differs from all the known southern African species of Riccia in the unique dorsal, hair like outgrowths from many of the epidermal cells and the large ± triangular scales, apically splitting into hair-like appendages.It is the type species of the new section.Micantes, so named because of the glistening dorsal covering.

FIGURE
FIGURE 4. -Distribution map of Riccia hirsuta in southern Africa.