Studies in the genus Riccia (Marchantiales) from southern Africa. 21. R. stricta, R. purpurascens and R. fluitans, subgenus Ricciella

Lindenberg (1836) regarded and published Riccia stricta as a variety of R. fluitans L. Subsequently, Nees (1838) and Gottsche et al. (1846) also treated it as a variety. Trevisan (1877) raised its rank and published the epithet, Ricciella stricta Trevis. Ricciella is, however, regarded as a subgenus; Ricciella stricta is, therefore, transferred to Riccia stricta (Lindenb.) Perold. It is described in detail and illustrated. R. purpurascens Lehm. & Lindenb., a related endemic species, is also more fully described than before and illustrated. R. fluitans L. apparently does not occur naturally in southern Africa. As far as is known, a single local specimen of it was introduced.

R. stricta grows on damp soil or mud, sometimes in association with other Riccia species, e.g.R. natalensis Sim, R. crystallina L. emend.Raddi, R. cavernosa Hoffm.emend.Raddi, and with Anthoceros spp.Occasionally it is aquatic and floats in masses on still water or is submerged.The land form of R. stricta sometimes forms bulbils at the apices of the thalli (Volk 1984) to survive drought conditions, and also to store food reserves; occasionally propagation is by ventral stolons (Figure IB).R. stricta is widely distributed in the summer rainfall area and is one of the commonest Riccia species in southern Africa (Figure 4).Its range extends further north wards into central Africa: Arnell (1956) reported it from Masai Province in Kenya, and Stephani from Usambara as R. fluitans (Stephani in Brunnthaler 1913) (see also 'Specimens examined').
Like the other members of the R. fluitans complex, R. stricta is highly sensitive to the water supply and humidity.It is therefore very variable in its morphology, the thalli generally ranging from thicker and narrower (Figure IE) in drier localities, to thinner and wider (Figure IF) in wetter places.
It is well known that species in the R. fluitans complex are very variable and notoriously difficult to distinguish from one another, ideally requiring cultivation under similar conditions (Berrie 1964).In Table 1, R. stricta is Markham (pers.comm.)found a wide range of flavonoid compounds in a specimen of R. stricta (S.M.Perold 2611), most of which he had reported (Markham et al. 1978) for R. fluitans; in fact, no components were found in the specimen by which it could be distinguished chemically from R. fluitans.This serves to confirm the close relationship of the two species.R. fluitans L. sensu stricto does not appear to occur naturally in southern Africa.A single specimen of it, leg.
Stephens BOL 25511, collected in a fishpond in Rondebosch, Cape, was apparently introduced along with other aquatic plants from Europe (note on packet in Schelpe's handwriting).None of the other southern African specimens that were examined, had the same appearance as this, which has somewhat thinner thalli, shorter branches and smaller air chambers with more distinctly visible walls, when viewed from above; dried plants have a slightly 'crinkled', not smooth, appearance (for differences between the species, see Table I).Earlier reports of R. fluitans from southern Africa by Krauss (1846), Stephani (1913), Sim (1926) (as R. fluitanslimicola), and Arnell (1963), have not been verified.The checklist by Magill & Schelpe (1979) records it, and is referred to by Mahu (1985) as proof of its presence in southern Africa.This list, however, was a preliminary account largely based on previous records.
Much of the tropical African material identified as R. fluitans or R. fluitans sens.lat.may also belong to R. stricta.Jones (1957) found that the spores of two of his African collections (655 and 826) named R. fluitans sens, la t., differed from those of European material and Bizot et al. (1978) concluded the same for material from Kiliman jaro.The spores illustrated by Jones (1985) (Foster 55 from Kampala, Uganda, and Jones 826 from Luki, Zaire) show a pronounced triradiate mark on the proximal face and thick areolar walls on the distal face, strongly reminis cent of those of R. stricta . Vanden Berghen (1972) who examined some African collections of the complex (Symoens 12436, 12774, Schmitz 7305 and Jean Louis 4410-all in BR) expressed the opinion that 'R .stricta e 5 8 00 "5 £ 00 O " ,fc o t.
Schmitz 7305 and Jean Louis 4410 were also examined by me and their spores studied with LM and SEM.In both, the triradiate mark is pronounced and the areolar walls on the distal face are thickened.
In spite of the uncertainty concerning the classification of the R. fluitans complex, a number of new species have been described in the group in recent years.Examples are: R. rhenana Lorb.( 1934 R. media Klingmiiller (1957); R. abuensis Bapna (1962) from India; R. limicola Jovet-Ast (1978) from Galapagos; and from Australia, R. luticola Na-Thalang, as well as two varieties of R. duplex and several of R. multiflda, all by Na-Thalang (1980).In a new species described from Brazil, R. jovet-astiae (Vianna 1988), the SEM micrographs of the spores are very similar to those of R. stricta and the differences cited by Vianna between this new species and R. stricta are not all significant, for example, specimens of R. stricta are not dioicous, but definitely monoicous, although in recently cultured material, antheridia and archegonia were consistently found in separate plants; the spore size exhibits a wide range in the many fertile southern African specimens examined (although Arnell's (1963) figure at 4 0 -5 0 pim, seems a trifle on the small side); the thalli are certainly not always markedly wider at the sporangia either.The thallus branches in R. jovet-astiae, however, appear to be rather shorter than in R. stricta.R. stenophylla Spruce, one of the 'older' species in this? group, also seems to be closely related to R. stricta.This is confirmed by examination of the spores of Volk 82/895 from Rio, identified as R. stenophylla.These spores are indistinguishable from three specimens in PRE identified as R. fluitans: Schijjner 1873/74 (Java), Verdoom I X 1930 (Java) and Wright CH 810 (? Cuba).
To conclude, perhaps one should bear in mind M eijer's (1958) words of caution, to postpone future splitting of this cosmopolitan species complex, R. fluitans, until more detailed studies, based on living material from many parts of its whole range, have been made.R. stricta, of course, is not a new species but merely a new combination.
R. purpurascens grows on damp, sandy soil or on mud, sometimes on streambanks and rarely in light shade, occasionally in association with other Riccia species, such as R. cupulifera Duthie, R. bullosa Link ex Lindenb., R. crozalsii Lev. and R. limbata Bisch.ex Krauss as well as with Fossombronia spp.and Gongylanthus spp.It is en demic to the north-western, south-western and southern Cape, which are winter rainfall areas (Figure 4).Arnell (1963) reported R. purpurascens from Victoria Falls.
Zimbabwe, but these specimens were actually R. stricta and had been misidentified.as were several others at PRE.The deep purple colouration that thalli of R. stricta develop on exposure to the sun.may have led to this error.
R. purpurascens and R. stricta are two southern African linear' species with ventral sporangia, and both produce stolons.Although there is some overlap in their distribution in the southern Cape, they generally occupy distinct climatic areas, with R. stricta being far more widespread in the summer rainfall areas; R. stricta is also sometimes aquatic, whereas R. purpurascens is strictly terrestrial.In addition, they differ in their apices, scales, the strict dioicity of R. purpurascens, the vertically positioned sporangia in the latter, its larger-sized thalli as well as differences in the spore ornamentation, with the areolar walls thinner and usually incomplete on the distal face.
Oil cells were not found in the stolons of R. purpurascens as reported by Sim (1926); numerous starch granules are, however, present.
FIGURE 4. -Distribution map of R. stricta, A ; and R. purpurascens, O , in southern Africa.