Studies in the liverwort genus Riccia (Marchantiales) from the south-west Cape

A new species of Riccia, R. parvo-areolata Volk & Perold, as well as sporophytes and spores o f R. villosa Steph. ex Brunnthaler, are described. Earlier descriptions of R. villosa were based on sterile plants. The unique structure o f the dorsal epithelium consisting of loose cell pillars in these two species (and also present in allied species grouped together in the section Pilifer) is described and illustrated. Riccia parvo-areolata Volk & Perold, sp. nov. Dioica (?), perennis, singulares vel subgregaria. Gametophytum mediocra ad 10 mm longa, ad 5 mm lata, ad 1,3 mm crassa, oblonge-ovata, in sicco subalbido-viridis, fissurata-tomentosa, in tumido pallide-viridis, subnitida, velutina; furcis brevibus, divergentibus, lata rotundato-truncatis breviterque emarginatis, apice sulcatis, ceterum convexis marginibus deflexis, costa subplana, viridis vel rare purpureo-maculata, in sicco apicibus contractis, squamis obvelatis breviterque sulcatis ceterum lata concavis, marginibus elevatis, subtus lunatis. Squa­ mae excedentes hyalinae, ad 600 |im magnae, semiorbicularae, basi plus minusve rare purpureae, confertae, integerrimae, cellulae longiusculae, ad 120 x 50 magnae, 5 7 angulosae, parietibus rectis. Frondis adultis sectio transversalis fere (2—) 3 —4-plo latioribus quam altis, stratum piliferum (epithelium) ca Vó, stratum aeriferum 3/6—4/6, stratum penarium 2/ó altitudine frondis; pili liberi, hyalini, conferti, (3—) 4 cellulae tumidae seriatim, ad 200 fxm longi, 60-90 jmi crassi, cellulae terminates obconici vel mamillati; columnae strati aeriferi ad 600 fj.m longae, 8—12 cellulae seriatae; canalabis aeriferibus 4 7 ( 8) angulati, perpendicularibus vel gradatim extrorsis inclinatis et apice versus oblique adscendentes, canalos aeriferos includentes. Antheridia et archegonia non visa. Sporangia matura libera, 400-900 sporae continentia; illae fuscae, subtriangularo-globosae, 70—85—96 Hm in diametro, alae angustae, minutissime erenulatae, poribus inconspicuae, distaliter parvo-areolata, inde nomen, 18—24 foveoli in diametro, anguli reticuli minute papillatae, proximaliter tres facettae parvo-areolatae subdistinctae limitatae. Chromosomata n =8 (Bornefeld) Riccia albomarginatae subsimilis, sed differet inter aliis ab colore pallido-viridis, cellulae pilorum crassiorae et ornatio sporarum parvo-areolata. Habitat in pascius (?) temporaliter humidis, subarenosis, acidis, expositis radiatonis. TYPE.— Cape, 3318 (Vanrhynsdorp): near Doringbaai, W of Vredendal, Kliphoek farm, gravel on sandstone ( —CD), J. M. Perold 23 (PR E, holo.). * Botanische Anstalten d. Univ., Wurzburg D 8700, Germany. ** Botanical Research Institute, Department o f Agriculture, Private Bag X101, Pretoria 0001. Dioecious?, perennial, single or in loose patches. Gametophyte medium-sized, segments up to 10 mm long, 5 mm broad, 1,2 mm thick; shape broadly oblong-ovate; seldom branching, and then branches short, divergent; dorsal surface when wet pale green, slightly glistening, velvety, apex roundly truncate and shortly emarginate, grooved apically, otherwise convex with downward sloping margins (Fig. 1.2, 1.3); in dry state dorsal surface greenish-white, felt-like, apex inflexed and groove covered by scales, otherwise broadly concave with margins ascending, nearly acute (Fig. 1.1); ventral surface slightly convex, green, occasionally flecked with violet. Scales semi-circular (Fig. 1.10) projec­ ting above margin, size up to 600 fim hyaline, base flecked with wine-red, imbricate, erect, margin smooth, with cells elongate, 5 —7 sided, straightwalled, size up to 120 x 50 ftm. Thallus in transverse section ( 2 ) 3 4 times broader than high, epithelium about J/6, assimilation tissue 3/6 to 4/ó, storage tissue 2/6 the height of the thallus (Fig. 1.3); dorsal cell pillars (Fig. 2.2, 2.5, 2.7) free, hyaline, about 200 jim long with ( 3 ) 4 inflated cells 60-90 |im wide, terminal cell mamillate or bluntly conical; assimilation tissue about 600 |*m thick, columns 8—12 cells deep, enclosing 4 —7 ( —8)-sided air canals, rising vertically or frequently sloping towards the sides or the apex (Fig. 1.3); the canals in the centre of the thallus narrow (Fig. 1.8) and enclosed by four cell columns, while those nearer the margin are broader and enclosed by 5—8 cell columns (Fig. 1.9); storage tissue cells often with oil droplets. Antheridia and archegonia not seen. Sporangia when ripe lie freely in the decaying thallus and contain about 400—900 spores. Spores (Fig. 3.1—3.6) rounded, triangular-globular, brown, size 70—80—90 fxm with narrow crenulate wing and inconspicuous pores at marginal angles, distal face with ornamentation finely areolate (hence its name), 18—22 areolae across the diameter, the corners of the areolae with short papillae; proximal face with three finely areolate facets, not sharply demarcated (Fig. 3.1). Chromosome number: n = 8, (Fig. 1.11, Borne­ feld). Their shapes are similar to those of R. albomarginata and R. albovestita (habil T. Borne­ feld, pers. comm). Riccia parvo-areolata colonizes exposed open 118 STUDIES IN THE LIVERWORT GENUS RICCI A (MARCHANTIALES) FROM THE SOUTH-WEST CAPE

Chromosome number: n = 8, (Fig. 1.11, Borne feld).Their shapes are similar to those of R. albomarginata and R. albovestita (habil T. Borne feld, pers.comm).Apparently the species is endemic to the western Cape.Together with R. albovestita Volk.R. albomarginata Bisch.emend.Sim, R. villosa Steph., R. concava Bisch.emend.S. Arnell and other as yet undescribed species (R. sarcosa ined., R. duthieae ined.) it belongs to a group of species which Volk (1983) has grouped together in the section Pilifer.They are characterized by a dorsal covering epithelium of free hyaline hair-like cell pillars (Figs 1.6,1.7 & 2 .7 ).This epithelium is mostly very fragile and can hardly be preserved.It is therefore rarely reconstituted in herbarium material and then only by using chloral hydrate, lactophenol or KOH.Even when fresh material is transferred to dilute alcohol, these cell pillars collapse.The cell walls are also not easily wettable and the resistance to water remains even after fixation in a mixture of alcohol-acetic acid (Volk, 1984).The composition of the cell walls is unknown.The zinc chloride-iodine reaction for cellulose is negative.

Riccia parvo-areolata colonizes exposed open
These free dorsal pillars are lacking in species of the Lichenoides, where the dorsal epidermal cells are not free standing and almost always arranged in parallel lines -an arrangement which is revealed in species of the Pilifer group only on horizontal sections through the chlorenchyma (Fig. 1.8, 1.9).The structure of the epithelium was studied with the light microscope (LM) as well as with the scanning electron microscope (SEM) using living material prepared by the usual procedure of critical point drying.At low magnification tangled, furry dorsal cell pillars are seen from above (Fig. 2.1).At high magnifications cells of the pillars of R. parvoaerolata are found to be extraordinarily variable in shape (Figs 1.6, 1.7 & 2 .2-2 .7 ).The terminal cells of the variably wide (25-90, but mostly 4 0 -5 0 tun) pillars are mamillate (Fig. 2.2), vermiculate (Fig. 2.3) to conically inflated (Fig. 2.5).Measurements of a large number of terminal cells of the pillars from different thalli revealed a length : breadth ratio of 1,2 : 1, where the length varied between 25 -49 -15 fim, and the breadth between 2 4 -4 0 -77 [im (average value italicized).The rest of the cells of the epithelium have similar dimensions (Table 1).
Riccia parvo-areolata is somewhat similar to R. albomarginata but differs from it in the pale green colour, the size of the epithelial cells and the finely areolate ornamentation of the spores.Older collections of a number of R. parvo-areolata specimens were incorrectly identified as R. concava.I'his is not surprising as in the dry state the thallus is pronouncedly concave (Fig. 1.1, 1.4) (Sim, 1926).R. parvo-areolata differs from R. concava in that it lacks radially arranged ridges in the ornamentation of the outer face of the spore, nor do the epithelial cells swell out again once they have collapsed.Dioecious?, perennial, in crowded gregarious patches, Gametophyte small, segments up to 8 mm long, 2,5 mm broad and 1,5 mm thick; shape narrowly oblong-ovate; single or furcate with branches diverging at an acute angle (Fig. 4.1); when wet dorsal surface whitish-green, apex bluntly obtuse; in dry state upper surface white, plane to concave; margins obtuse, flanks steep, often purple to nearly black; ventral surface light brown to purplish black, flat to slightly convex.Scales very prominent, projecting beyond the margin, closely imbricate (Fig. 5.1), laterally in one row, hyaline; when dry, white to yellowish, up to 1,8 mm long and I mm wide at base which is purple (Fig. 4.3-4.5);shape triangular-acuminate, margins denticulate apically, frequently ending with a narrow caducous terminal cell; most cells oblong-hexagonal, larger at the base and up to 110 |tm long and 40 uni wide, with straight thickened walls, cuticle striolate.Thallus in transverse section 1 -2 times broader than high (Fig. 4.2), epithelium about Vs to 2/s, assimilation tissue Vs to 2/5, storage tissue Vs the height of the thallus (Fig. 4.2); dorsal epithelium consists of colourless, nearly cylindrical free cell pillars ) 300 -700 tun long, each pillar composed of ( 4 -) 5 ( -6) fragile, tender cells which collapse easily, (4 0 -) 80-130 (-2 0 0 ) (.m long, (2 0 -) 3 0-50 (-7 0 ) uni wide, widening gradually towards base of pillars, 2 -3 times longer than wide (Table 2): below epithelium a layer of ehlorophyllose assimilation tissue about 250-400 (-6 0 0 ) tun deep, consisting of  ( -115) um in diam eter, colour brown to very dark brown or black (Fig. 6.1-6.6);distal face convex, ornamentation papillose to vermiculate, in a whorl which spirals from the centre outwards to the margin in 10-15 thick ridges (Figs 4.7 & 6.5); some spores, probably riper, have flattened ridges; proximal face with similar sculpturing, but ridges not in obvious spirals (Fig. 6.1 -6.3); apex blunt, triradiate mark not prom inent, each of the three suture lines of the mark term inate in a pore at the margin.
Most plants are sterile.Of eighteen specimens examined, only four were fertile, propagation usually being adventitious.R. villosa produces globular gemmae originating from the thallus and later perforating the epithelium of the older parts.This species is endemic to South Africa and known from several localities in the drier winter rainfall parts of the Cape like the Karoo, the Knersvlakte and Namaqualand.It grows at altitudes of 300-1 000 m in depressions, on sandy to gravelly non-calcareous soils, fully exposed to the sun and in association with small moss species, Desmatodon convolutus (Brid.)G rout, Oedipodiella australis (Wager & Dix.) Dix., with Mesembryanthemaceae Ruschia spp., Dactylopsis digitata (A it.)N .E .B r., Argyroderma spp., Conophytum spp., and with Crassula spp.R. villosa, with its free epithelial cell pillars, is a member of the section Pilifer.It is recognized by the large hyaline triangular scales.In drying out, the thallus margins curve inwards and the large scales meet and project upwards along the midline.This, together with the collapse of the epithelial cells, protects the living tissue of the thallus.It is a distinctive plant.A drawing of R. villosa appears on the cover of S, ArnelPs book on South African hepatics.

TABLE 2 .
-Measurements of the cells of the epithelium of R. villosa (in |«n) (Perold 20)