Studies in the Marchantiales ( Hepaticae ) from southern Africa . 5 . The genus Exomiotheca

A taxonomic account of the genus, Exomiotheca, and its local representatives, E. pustulosa and E. holstii, together with their distribution in southern Africa as currently known, is given. Exomiotheca megastomata is here treated as a synonym pt E. holstii since no distinct morphological differences could be found between them.

Thalloid.small to medium-sized to quite large, silvery glaucous green, dorsally with numerous conical evaginations of the epidermis; in crowded patches, in damp to rather dry, exposed areas on gravelly or sandy soil or on soil overlying rocky outcrops, xerophytic.Branches sim ple, or once, sometimes twice pseudo-dichotomously fur cate, apex entire to shallow ly notched, dorsally not grooved, slightly concave.Dorsal epidermis raised as pus tular or conical evaginations over low or tall air chambers, opening above via simple air pores, encircled by thinwalled cells and basally occupied by chlorophyllose, sometimes branched, cell filaments, the lateral walls ver tical, hyaline; storage tissue 'Ys or ± Vl the thickness of thallus, a rather loose mesh o f open, round spaces or socalled 'Schleim zellen' surrounded by sm aller angular cells, single oil bodies in scattered upper and lower cells; ventrally keeled to rounded, green to purple, flanks slop ing obliquely upward and outward; rhizoids some smooth, others tuberculate.Scales smallish to medium-sized, pur ple, oblong or rounded, occasionally with I or 2 append ages, otherwise large, hyaline with purple base, obliquely triangular, with long, filiform appendages from apex.
Monoicous or ?dioicous.Antheridia in rows along mid dle of thallus, in shallow groove where development of air chambers temporarily suppressed, sunken, necks pro truding conspicuously.Gynoecia raised on stalk with sin gle rhizoidal furrow, receptacle erect or horizontal, when hammer-like, the parenchymatous centre covered by air chambers that open via simple pores, above or laterally, with 1 or 2 capsules, each supported by a seta, exserted from bilabiate involucre and dehiscing by 4 or 5 valves after shedding operculum; otherwise subsessile, lacking stalk, central dome with air chambers above, epidermis extended laterally and turning purple, forming involucres that cover capsules on either side; capsule wall with cells containing semi-annular thickenings.Spores 70-75 pm or almost twice as large, ± 140 pm, triangular-globular, distal face with large hollow, conical papillae or convoluted areas covered with granules, proximal face without triradiate mark, heavily encrusted with granules; elaters taper ing, up to 150 Jim long and trispiral or blunt at one end, much shorter and unispiral or ringed.
M onoicous (or rarely ?dioicous).Androecia in 1-3 rows along middle of thallus, close to female receptacle (distal or proximal to it), antheridia sunken, their necks ± 175 |j.m long, protruding above surface between air cham bers, which are suppressed here to form a shallow groove (Figure 1 A).Gynoecia just proximal to bifurcation of 2 terminal branches, emerging as a central, round green cushion, at maturity raised on a cylindrical stalk (Figure 1C), basally purple-streaked, the remainder yellowish, length variable, up to 10 mm, diameter 350 |nm, with a single rhizoidal furrow, in transverse section (Figure IK) cortical cells similar to medullary ones, average size 25.0 x 17.5 jim, top of stalk loosely sheathed in a short col lar-like outgrowth of the head, the latter internally filled with parenchymatous tissue and covered by a row o f filament-containing air chambers that open via hardly raised simple air pores, laterally with a capsule exserted from bilabiate involucre on either side, 3 mm across and ham mer-like in appearance (Figure ID), frequently, however, bearing only 1 capsule above, when erect and oblong.Capsule sheathed in thin calyptra, ± spherical, wall brown, unistratose, upper part forming an operculum, cells some what smaller, otherwise similar to the rest, ± 57.5 x 25.0 |L im , spindle-or irregularly shaped with sem i-annular thickenings (Figure 1J), in transverse section 30 jim thick, with 'rods' projecting inwardly (Figure II).dehiscing by  Bothalia 24.1 (1994) 4 or 5 irregularly shaped valves and folding back, petal like, seta up to 1625 x 500 pm, with ± 30 rows o f cortical cells in transverse section, foot rounded.Spores 70-75 (L tn i in diameter, polar, triangular-globular, bright honeybrown, distal face (Figure 2A) rounded, with up to ± 50 crowded, hollow, conical papillae, 10 pm high and 10 pm wide, walls o f papillae composed of numerous adjoining granules stacked into tiny pillars in some areas and only exposed where wall has broken down (Figure 2B); prox imal face with vestigial triradiate mark or part of it occa sionally present (Figure 2C), entirely encrusted with fine granules (Figure 2D); wing absent, margin scalloped by protruding papillae on distal face.FJaters honey-brown, not tapering toward ends, up to 150 x 10 pm , trispiral.

DISCUSSION
As a member uf this rather rare genus Exormotheca, E. pustulosa is quite widespread, although the single, highly disjunct record from Mexico (Bischler 1976) may be an introduction (Gradstein et al. 1983).The latter au thors regard it as an Afro-American disjunct with a subtropical-M ed iterran ean range.It is know n from the follow ing M editerranean c >untries: Portugal, Spain, France (with only one locality (Bischler & Jovet-Ast 1981)) and Italy, as well as from the Atlantic islands: Azores, Madeira, the Canaries, Cape Verde and St Helena; also from two island groups (or islands) in the Indian Ocean: the Comores and Réunion (Bischler 1976).It is further known from Saudi Arabia, United Arab Emirates and Oman (Frey & Kurschner 1988) as well as from the following African countries: M orocco, Chad, Ethiopia, and also from Kenya, Tanzania (Bizot & Pócs 1979), An gola, Zimbabwe and southern Africa.In southern Africa (Figure 3) E. pustulosa has been quite rarely collected in Namibia (O.H. Volk pers.comm.), as well as in western, central, southern and eastern Transvaal, Orange Free State, Lesotho and southwestern Cape.Frey & Kurschner (1988) regard E. pustulosa as a xerothennic Pangaean taxon.They define the xerothermic Pangaean element as comprising representatives with a present pattern of distribution corresponding to the Perm otriassic con tin en tal P angaea region.Exormotheca pustulosa grows in association with other liverworts, such as Riccia species and Mannia capensis on soil around granite or sandstone outcrops, which are generally only temporarily wet.Under rather wetter conditions the ven tral scales are less conspicuous and almost entirely hya line.V eg etativ e re p ro d u c tio n is by v en tral tu bers (Knollchen) which were spherical, scale-clad, 500 pm wide structures in S.W. Arnell 791, one of only three southern African specimens that had mature sporophytes.Schiffner (1942) had already placed E. africana Steph. in synonymy under E. pustulosa, when Arnell (1953a) stated that he could not find any real differences between E. pustulosa a n d E. africana.The Indian species, E. tuberifera, described by Kashyap (1914), seems very closely related to E. pustulosa and so does E. ceylonensis M eijer (1956).Exormotheca pustulosa can be d istin guished by its low conical air chambers ± Vt, tilled with chlorophyllose cell filaments, by its small size, oblong or rounded purple scales, by its stalked carpocephala, by its spore ornamentation and by its spherical tubers.Thallus medium-sized to quite large, broadly linear to ± ovate (Figure 4A), silvery green, with numerous con spicuous, conical evaginations of the air chambers (Figure 5B, C), medianly narrow and somewhat lower, laterally mostly wider and taller, each opening above via an air pore (Figure 5A), dorsally flat to centrally slightly con cave or shallowly grooved toward apex, scales at margins, except at apex, mostly hidden when wet; concave to ap parently slightly grooved along midline of dorsal face, white, with hyaline, apical and distal scales incurved over margins or erect, when dry; in crowded patches, simple or once, rarely twice or 3 times pseudo-dichotomously furcate, symmetrical or not.Branches with total length 8-15(-22) mm, terminal segments generally 4 -7 (-1 0 ) mm long, moderately divergent, (2.5-)3.0-5.0(-7.0)mm wide, 2125-2900 |im thick; apex slightly tapering, with shallow notch, m argins obscured by air cham bers; ventrally rounded to flattish, green, or with transverse extensions of purple scale bases or entirely purple, flanks basally tinged with purple, sloping slightly obliquely upward and outward (Figure 4C) covered with large hyaline scales.Dorsal epidermal cells unistratose, hyaline, raised into 4 -6-sided air chambers, centrally 1000 x 150 |im and mar ginally 1500 x up to 500 fim, in 8 -1 2 irregular rows across width o f thallus, attached to each other at sides, but narrower apical part free (Figure 4E) for ± 250 |im, at margins o f thallus at least 500 |im at top free; cells mostly 5-or 6-sided (Figure 4E) near top o f elevated cones 65-75 x 4 2-50 jim, lower down elongated, 125-175(-260) x 30-50 jim , thin-walled, air pores at or near tip o f cone (Figures 4D; 5D), simple, rounded or elon gated, (80 -) 125-137 x 5 0 -7 5 (-8 5 ) |im , bounded by smaller cells, 75-112 x 2 7-30 |im, sometimes a single cell, ± 37 x 37 (im, or part o f a larger cell jutting into lumen of air pore; assimilation tissue 350-400 |iim thick, occupying basal VS-W of air chambers, and composed of densely crowded filaments (Figure 4F), 7 or 8 cells long, top cell with conical tip, 62.5 x 17.5 |im, others 67.5 x 32.5 |im , some filaments branching from near base, filled with chloroplasts; storage tissue 1000-1150 (im thick, cells forming a rather open mesh with 'rounded spaces', 150 x 100 jum, surrounded by smaller, mostly angular cells, ± 62 x 50 jim, toward the top and base of storage tissue and quite numerous, cells containing oil bodies, these transversely oval, 67.5 x 55.5 |im , yellow, not en tirely filling cells; ventral epidermal cells isodiametric or not, giving rise to rhizoids, some smooth, 17.5 |iim wide, others tuberculate, 12.5 (im wide.Scales imbricate (Figure 5E, F), large, 1250-1625 jim long, 900-1500 (im wide at base, hyaline but base purple, somewhat obliquely trian gular with vertical side ± entire, facing toward apex of thallus, diagonal side often toothed, cells in body o f scale long-hexagonal, 225-250 x 37-62 (im, smaller at base, lacking oil bodies, apex mostly with branched or un branched, filiform appendages up to 5 (Figure 4G), 700-1000 |im long, cells 150 x 20 |im.
M onoicous or dioicous or ?protandrous, rarely produc ing gametangia of both sexes simultaneously.Androecia in 2-4 irregular rows along midline of thallus (Figure 4B), in 1 or 2 successive linear groups, antheridia sunken, necks protruding conspicuously, ± 1000 |im, between cen tral air chambers, development of the latter here tempo rarily suppressed.Gynoecia developing near apex of thallus (which continues growth), causing widening and hollowing of latter, somewhat sunken, sessile, mostly in single groups (Figure 4A) ± 4 mm wide, occasionally with a second one behind the first, supported on central core of dense parenchymatous tissue, 1500 jim wide, on either side l(or 2) slightly obliquely held capsules, 1500 |xm wide, wall with cells containing semi-annular thickenings (Figure 41, J), on short seta, 500 x 550 |im , ± oval in shape, cortical cells hardly differentiated from medullary ones (Figure 4K), sheathed in thin calyptra, capsules sep arated by taller central dome, ± 2250 |nm wide, containing elongated air chambers (Figure 4H), basally with cellular filaments and opening above via simple air pores, sur rounded by thin-walled cells, and otherwise covered by larger cells with thicker, purple-stained walls; covering layer of dome forming a groove laterally and continuing on both sides as deeply purple-stained extensions; the in volucres, containing numerous cells with oil bodies, partly covering capsules and at scalloped margins with smaller, thinner-walled cells.Spores 117.5-142.5 \xm in diameter, polar, triangular-globular, dark red, distal face (Figure 6A) rounded, with 6 -8 highly convoluted, raised areas across, 22.5-27.5 |im wide, bordered by superimposed layers of granules and hollowed in the centre, distinctly or poorly separated by deep furrows (Figure 6B); proximal face with triradiate mark absent (Figure 6D), but with slight flatten ing of the 3 facets, entirely encrusted with numerous, tiny granules; wing absent (Figure 6C, E), margin scalloped by projecting convoluted areas from distal face.Elaters brownish red, tapering slightly at one end, blunt and thicker at the other, 70-90 x 20 |Lim , unispiral or ringed (Figure 6F).Chromosome number, n = 18, 32 (T.Bomefeld pers.comm, via O.H. Volk).

DISCUSSION
Exormotheca holstii and E. pustulosa are the only two species belonging to this rather rare genus, that also occur in southern Africa.Exormotheca holstii has been reported in southern Africa (Figure 3) from Namibia [several col lections recorded by Volk (1979)].Botswana, northern, central, eastern and southern Transvaal, Natal, Orange Free State and northern Cape Province.Most gatherings are from the Transvaal, as in recent times it has become a more thoroughly collected area, as far as bryophytes are concerned.Exormotheca holstii has also been found else where in Africa, namely Tanzania (locus classicus) and Zimbabwe (Best 1990).It appears to prefer quite dry, somewhat sandy or gravelly soil, sometimes between grass or in exposed areas that are only occasionally wet and that overlie sandstone or quartzitic or granitic rock.It sometimes grows in association with Riccia species, such as R. volkii, R. rosea and R. albovestita.Marquand (1930) described a new species of Exor motheca, E. megastomata, based on a sterile specimen from Middelburg, Transvaal.This plant and its scales are somewhat larger than in E. holstii Steph., but the ratio of the surface area of an apical scale to that of a section of the thallus, works out to the same for both; no other sig nificant differences between E. megastomata and E. holstii could be found after careful study of the type specimens of both species.I, accordingly, regard them as conspecific and place E. megastomata in synonymy under E. holstii.Marquand stated that E. megastomata 'is distinct from all previously described species of that genus in the very tall  Bothalia 24,1 (1994) Arnell (1963) later placed E. youngii in synonymy under E. holstii.In his key to three species of Exormotheca, Arnell (1963) also referred to the air chambers in E. holstii as being free almost to the base.This is contrary to my findings (see above).Stephani (1899) also described the stomata (sic) of E. holstii as 'densissima altissima, ad Vt, coalita, tertio supero libera', and Schiffner (1942) re ferred to the air chambers as 'seitlich bis drei Viertel verwachsen'.Am ell's observations must, therefore, have been based on an error.In Schiffner's (1942) monographic study of the genus Exormotheca, he makes no reference to E. megastomata.In this work he refers to the contro versy between himself and Muller (1940Muller ( , 1941) ) concern ing the application o f the epithet, E. bullosa, which he suggested 'als Art einzuziehen ... ist'. 1 discussed this in greater detail in Perold (1991), urging a return to its earlier epithet, E. welwitschii, and furnishing reasons for it.
Fruiting collections of those Exormotheca species that are characterized by sessile carpocephala, are extremely rare and have only been illustrated once before by Douin & Trabut (1919).They described Corbierella algeriensis, a synonym of E. algeriensis, as dioicous.O f the speci mens studied in the present work, Giess 15383 is defi nitely monoicous; o f the remaining 53 specimens, only the type specimen of E. holstii, Holst 3107, Volk 01160 and Gennisliuizen 2839 have mature sporangia and are dioicous or possibly protandrous.
Volk (in litt.)identified his collection Volk 81/015, from Middelburg (the type locality of E. megastomata), as E. megastomata-, Bomefeld (in litt.)found its chromosome number to be n = 18, whereas specimens from Namibia have n = 32 chromosomes.Bomefeld and Volk are of the opinion that the material from M iddelburg and from Namibia represents two different species.However, two different chromosome numbers manifested here are not reflected in morphological differences.The same phenom enon w as observed in som e Riccia sp ecies, e.g.R. argenteolimbata (Volk et al. 1988), where as many as five chromosome numbers were found in the same species.
Exormotheca holstii can be distinguished from other species in the genus by its large size, by its tall air cham bers, basal •/5-1/3 occupied by chlorophyllose filaments, and laterally adjoined except for the apical 250 Jim toward the centre of the thallus and marginally for the apical ± 500 jim; by the large, hyaline, triangularly shaped scales with long filiform appendages and by its subsessile gynoecia.Tubers were not found.
for chrom osom e counts.The curators of BOL, G and NY are thanked for the loan o f type specimens.My thanks also to my colleagues at NB1 for collecting specimens, to the artist, Ms A. Pienaar, the typist, Mrs J. Mulvenna and the photographer, Mrs A. Romanowski, for their valued contributions.
FIGURE4.-■Exormotheca holstii.Anatomy ol thallus.A, thallus w ith sessile carpocephalum from above; B. thallus with antheridial necks emerging between air chambers in midline; C, transverse section of thallus showing tall air chambers, chlorophyllose cell Filaments and storage tissue; I), air pore and surrounding cells from above; E, top part of two partly adjoining air chambers; F. assimilation tissue with cell Filaments; G, scale with branched filiform appendages; H, carpocephalum, upper half three dimensional, lower half in transverse section; I. capsule wall from above; J, capsule wall in transverse section; K. transverse section o f seta.A, H, K. (iermishuizen 2839; ( '. Perold < Sc Koekemoer 2S72\ D, S.M. Perold 2702: E, F, Glen 2I90\ G, I. J. Holst 3107.Scale bars: A -C , II. 1 mm; D-F, I-K. 100 pm ; G. 5(H) Jim.Drawings by A. Exormotheca holstii.Thallus, A, lhallus f rom above, wiih eonieal air chambers; B, air chambers seen from side; C, air pores seen from above; D, air pore at apex of cone; E, scales inflexed over apex of thallus; F, scales seen from side.A -F, R. Smit s.n.