Studies in the liverwort family Aneuraceae ( Metzgeriales ) from southern Africa . 1 . The genus Aneura and its local representative

This is the first of several projected articles dealing with the southern African Aneuraceae H.Klinggr. The family is cosmopolitan and comprises two subfamilies, only one of which, the Aneuroideae. with two genera. Aneura Dumort. and Riccardia Gray, occurs locally. Because o f the taxonomic problems associated with this family and the scarcity of fruiting material, only one taxon in the genus Aneura, A. pinguis (L.) Dumort., has so far been accepted in this treat­ ment. This is not meant to imply, however, that A. pseudopinguis Herzog does not occur in southern Africa: only, that the specimens I have examined, all belong to A. pinguis. A description and illustrations of A. pinguis. together with a distribution map are provided.

In both genera there is little anatomical differentia tion.usually without any distinction between the wings and midrib or nerve (the epithet Aneura.signifies the absence of a nerve).Because of their simplicity in organ ization.there are few distinctive characters.Moreover, frequent variability, apparently environmentally induced, in those few features that are available, make them diffi cult to study.Taxonomically it is w idely accepted that the Aneuraceae is one of the most troublesome families among the Hepaticae.
The long, narrow thalli of Riccardia species in particular, often grow in intricately intertw ined.densely overlying mats, with more than one species sometimes being pre sent.The branches are rather brittle, and unravelling and cleaning them for study needs to be done w ith care and is time-consuming.Sterile plants are of little value, as gametangial and sporophytic characters are necessary for the correct placing of specimens: unfortunately, they are frequently w ithout sporophytes.although they may pro duce gametangia.Furthermore, as they soon disappear, the oil bodies in samples from fresh plants, that are preferably kept in a refrigerator at 5C -6°C, need to be photographed and studied as soon as possible after col lection.Data from disintegrating oil bodies can be mis leading.
It is also recommended that plants should be studied in cultivation.Meenks (1987) is of the opinion that herbarium collec tions are often useless, particularly if they are more than 20 years old.Type specimens are.however, far older gen erally, yet one needs to study them to compare them w ith fresh, living collections, however difficult that may be.It is accordingly considered necessary to revise at least the southern African members of the Aneuraceae, which often represent southern extensions of range, and to give good illustrations wherever possible.This publi cation is the first in a series of projected papers on the local Aneuraceae.

METHODS AND MATERIAL STUDIED
With some exceptions, the same methodology as was employed in my treatment of southern African Fossombronia species (Perold 1997), is followed here: 1. sam ples of field-collected specimens were fixed in FAA on the day of collection; 2, more samples were selected for oil body study and cultivation and initially kept at 5°-6°C in transparent screw boxes, lined with damp fil ter paper; and 3, the rest of the specimens, destined to be held in the herbarium, were allowed to air-dry rapidly.Aneura pinguis is subcosmopolitan in its distribution and has been reported from many localities worldwide; South America and Australia are, however, excluded.It is also present in southern Africa, but is infrequently col lected (Figure 2 but there appears to be some overlap in the characters assigned to these two species in our local specimens.Meenks & Poes regard A. pinguis as having opaque thal li.medianly (9)10-20 cells thick, with relatively short male lobes, which seldom branch and contain 2-5(6) pairs of antheridia; the spores are 20-25 (jm diam.On the other hand.A. pseudopinguis thalli are, according to them, translucent, medianly only 5-8(9) cells thick, the male branches are longer, often with 3 (seldom 4) rows or 7-10(-20) pairs of antheridia.and the spores are 13-16 jam diam.
In the specimens they studied.Gradstein et cd. (1983) regarded the identity as confirmed in 'only the records of plants possessing either male branches or spores'.They also report that in African samples of A. pseudopinguis 'usually only one sex is found in a particular locality'.This is contrary to the findings in our two fertile collec tions referred to above, and may provide further evi dence that we are dealing with A. pinguis.
In 1952 Amell reported his new' Riccardia subtnarginata from Deepwall Forest Reserve.There were no mature capsules with spores, but the median cross sec tions of the thalli were given as 15 cell rows thick.In my examination of Amell's specimens the median cross sec tions of the thalli ranged from 8-13 cell rows thick.
As already remarked in the paragraphs on 'Historical notes', Amell had admitted to Jones (1956) (1926,1928) showed that, so-called 'races' of the holarctic populations were, in some cases intersterile.the matter of how to define this species has been highly uncertain'.Furthermore, it seemed most unlike ly to Schuster that a species could occur in the Arctic polar desert of Ellesmere Island and also in tropical and subtropical areas.He concluded this paragraph with the following observation.'Recent study has also shown that the tropical American-African plants formerly referred to A. pinguis represent A. pseudopinguis Herz'.
According to Meenks & Poes (1985).however, both taxa occur in East Africa, as well as in West Africa (Gradstein et al. 1983)
. but A. pinguis appears to be rarer in tropical Africa than A. pseudopinguis.In southern Africa.A. pinguis is very infrequently collected and fer tile plants are the exception by far, rather than the rule; this scarcity of fruiting material further complicates the study of these plants.To quote Proskauer (1971), 'Riccardia pinguis, a species which we have long known to present a nightmarish problem .... probably requiring more than a single lifetime of research for a minimum understanding'.Stephani (1899) placed R. latissima (Spruce) Schiffn. in synonymy under R. pinguis.However.Meenks & De Jong (1985) note that, the oil bodies in A. latissima are bright brown, not clear and colourless, as they are in A. pinguis.Furthermore, a chromosome no.n = 8, has been reported by Nakata & Inoue (1989) for A. latissima.whereas the chromosome no.n = 10 is given for A. pin guis.Stephani's synonymy of A. latissima under A. pin guis, is, accordingly not accepted here.