Studies in the genus Riccia ( Marchantiales ) from southern Africa . 24 . R . moenkemeyeri , subgenus Ricciella : new records

Riccia moenkemeyeri was twice described by Stephani (1887, 1891), the second time as R abnormis. Amell (1952) described it as R. undulata. It is clearly a plastic species (Jones 1957) and is widely distributed in tropical Africa, from Sierra Leone (as R. undulata), Nigeria, Cameroon and into the Congo Basin. Until recendy, Sim’s specimens from the Matopos in Zimbabwe, were the most southerly records known, but the species has now also been collected in southern Africa, just east o f Pretoria and at Kransberg, in the western Transvaal.

Riccia moenkemeyeri is a tropical African species, known from Sierra Leone (as R. undulata), Ghana, Nigeria, Cameroon, the Congo Basin, (Region du Lac Moero (Vanden Berghen 1972)), Angola, Zimbabwe, Malawi, and now also with outliers into the Transvaal, southern Africa (Figure 3).Its presence on Fernando Po, as reported by Stephani (1887) for the type specimen, Moenkemeyer 5, must have been a mistake, as the locality on the label states that it is from Calabar, Niger, and in Species hepaticarum (Stephani 1898) it also does so.
The species grows in damp places, on rich loamy soil, mostly near streams and in association with other Riccia species (in southern Africa) such as R. stricta (Lindenb.)Perold, R. atropurpurea Sim and with Exormotheca pustulosa Mitt.
Riccia moenkemeyeri is characterized by a more or less persistent dorsal epidermis which is marked out into small areolae, each with a small central air pore; by numerous, narrow air chambers, appearing to be in more than one layer; by undulating thallus margins which terminate in a single row of hyaline cells and by a highly distinctive spore ornamentation with 8-10 large areolae on the distal fece and numerous tiny areolae on the proximal face which lacks a triradiate mark.
According to the classification used in previous papers in this series, R. moenkemeyeri is placed in subgenus Ricciella, section Spongodes, on account of the presence of air chambers in the assimilation tissue.Although not truly growing in rosettes, it would be more properly placed in the informal group 'Crystallina', together with R. crystallina L. emend.Raddi, R. cavernosa Hoffm.emend.Raddi and R. cupulifera A.V. Duthie, than in group 'Vesiculosa' with R. bullosa Link ex Lindenb., R. garsidei Sim, R. volkii S. Arnell and R. rubricollis Garside & Duthie ex Perold, which mostly have rather 'swollen' thalli with large, inflated air chambers.The oblique orientation of the ventrally protruding sporangia is a character which it apparently shares only with R. stricta (Lindenb.)Perold, but the latter species has long, narrow, ribbon-like branches and is placed in subgenus Ricciella, section Ricciella.
The specimen, S.M. Perold 2603, collected in March 1990, appeared to consist of male plants only, but on serial and longitudinal sections of several branches, it was found to also have young, deeply imbedded archegonia with long necks that are, however, not visible from above.Mature antheridia have necks up to 375 /xm long, but in young antheridia they are considerably shorter.Dr E.W. Jones  kindly examined part of my collection and commented on the antheridial necks being shorter than 100 /xm.He also found (pers.comm.) that West African specimens of R. moenkemeyeri are only exceptionally without spores, the branches are longer and less divaricate and the epidermis is more persistent.The Condy 22 and 23 collections were gathered in April 1991, (slightly later in the following season than my specimen) and both had sporangia with mature spores.Seventeen months after collection, a sample of S.M. Perold was kept damp for a few days in a Tupperware dish and it soon resumed growth.Jones (1957) reported R. moenkemeyeri to be a very plastic species, a wide range of forms occurring in a single site.He regarded R. chevalieri Steph.as closely resem bling R. moenkemeyeri in vegetative features; the type specimen, Chevalier 88, however, only had 'a few male inflorescences but no female', and its identification could thus not be confirmed by spore ornamentation.
Riccia undulata S. Amell was placed in synonymy under R. moenkemeyeri by Jones (Jones & Harrington 1983), although Arnell (1952) reported the fronds to be up to 7 mm wide, which is much wider than the measurements (2.0-2.5 mm) given by Jones (Jones & Harrington 1983) for the type specimen.The spores of the two species are identical, however.Jovet-Ast (1975) reported on spore germination and development of the protonema in R. moenkemeyeri, con cluding that the various stages (quadrant, plate and column formation) were similar to those in R. cavernosa.
The reason for the discrepancy in the chromosome counts of R .moenkemeyeri as reported by Bomefeld (pers.comm.) and Jovet-Ast (1969), has not been ascer tained.Jovet-Ast maintains that in Riccia, n always equals 8 or multiples of 8. Jovet-Ast (pers.comm.)expressed surprise that Bomefeld's (1989) counts do not agree with hers and suggests that Bomefeld's counts be verified.Bomefeld (1984) postulates that the different chromosomes of the basic set in Riccia, which he identifies as A, BB, CC, DD and E, can multiply heterogeneously (for which he has coined the term 'nothopolyploidy'); this would explain how aberrant numbers could arise.

FIGURE
FIGURE 3. -Map showing distribution of R. moenkemeyeri in southern Africa.