Nomenclatural changes and additions to the genus Ophioglossum in Africa ( Ophioglossaceae : Pteridophyta )

Recent research has necessitated a review of the nomenclature of the genus Ophioglossum in Africa. This paper establishes a new species, O. caroticaule J. E. Burrows, a new subspecies, O. vulgatum L. subsp. africanum Pocock ex J. E. Burrows, and a change in status, O. latifolium (Prantl) J.E. Burrows (basionym: O. gomezianum var. latifolium Prantl). Lectotypification is provided for O. gracillimum Welw. ex Hook. & Bak., O. lusoafricanum Welw. ex Prantl, O. latifolium (Prantl) J.E. Burrows, and 0 . rubellum Welw. ex A. Braun. Nomenclatural problems in O. lancifolium Presl are discussed.


INTRODUCTION
The genus Ophioglossum L. has received no taxonomic attention in Africa since Clausen's (1938) confusing monograph of the genus.The simple morphological struc ture of the plants together with apparently considerable intraspecific variation has caused compilers of African re gional floras to either follow Clausen's nomenclature or assume a conservative stance by maintaining broadly cir cumscribed species which, in the light of recent studies, are often composed of two or more clearly distinct taxa.
The most important development since Clausen's work is the publication by Wagner & Wagner (1983) of their 'genus communities' concept, based upon work on the genus Botrychium Swartz (Ophioglossaceae) in North America.This concept made use of the fact that Botrych ium (like Ophioglossum) frequently grows together in multiple species communities and, when this occurs, one is able to make rational comparisons between taxa occur ring within a community, particularly if these differences are maintained in communities found elsewhere under dif ferent edaphic and climatic conditions.This concept has provided taxonomists w ith a valuable additional tool with which to distinguish between environmentally-induced variation and differences that are genetically controlled.
During recent studies, the senior author has discovered an unique area in northwestern Zimbabwe which supports 11 species of Ophioglossum.Additional genus communi ties have since been located in both Zimbabwe and South Africa which have made a better delimitation and defini tion of the southern African species of Ophioglossum pos sible.However, these studies have resulted in the need to revise the nomenclature of several of the taxa occurring on the African subcontinent.

DISCUSSION
In 1983, the senior author collected nine species of Ophioglossum growing within an area of about six square kilometres in the Sengwa Wildlife Research Area of north western Zimbabwe.Subsequent collecting at Sengwa has yielded a further two species, bringing the total to eleven, a situation not recorded to date elsewhere in the world for the genus Ophioglossum.Additional genus communities have been discovered by the senior author on Ngomakurira.northeastern Zimbabwe (6 species), Elim Hospital, eastern Zimbabwe (4 species), Treur River, eastern Trans vaal (5 species) and several communities composed of two or three species each.These localities occur on var ious substrates (sandstone, granite, quartzite and dolomite) and under varying climatic conditions, and the consistent differences displayed between members of these genus communities have allowed for clearer definitions to be established between taxa.
However, the specific concepts within the African members of Ophioglossum entrenched by Tardieu-Blot (1953, 1964) and Schelpe (1970Schelpe ( , 1977) ) do not adequately cover the number of taxa that are evident from genus com munity studies.This was noted by Dr Mary' Pocock of Grahamstown who spent much time studying the South African species of Ophioglossum.She recorded her con cepts in a manuscript which unfortunately was never pub lished.The author's studies corroborate some of Pocock's species concepts and one of her taxa is published below.

The
Ophioglossum caroticaule appears, from the few known collections, to be a species of shallow, sandy or humic loams which are seasonally moist or wet, growing among sparse, short grasses in subtropical deciduous

1.2.
Ophioglossum gracillimum Welw.ex Hook.& Bak., Synopsis filicum: 445 (1868); Burrows: 40 (1990); Johns: 8 (1991).Type: Angola, Pungo Andongo, near Catete, Jan. 1857, Welwitsch 36 (BM, lecto.!; K!, LISU, iso.).Although the collection Welwitsch 36 is repeatedly quoted as the type material of this species, no single ele ment has been selected from what are, by Welwitsch's own admission (on the BM sheet), several different collec tions, albeit from the same area or locality.After his initial gathering in January 1857, to which he allocated the num ber 36, Welwitsch apparently re-collected this species on three occasions.Subsequent collections made in February were then numbered 36a, 36b and 36c and the BM sheet bears plants from all four gatherings.Since the January collection (No. 36) is the first collection, and is typical of the species, the group of seven central plants immediately above the brown label on the sheet housed in BM, is hereby selected as the lectotypic element for the name of the species, with isotypic specimens in K and LISU.
Soon after the publication of Welwitsch's epithet, the taxon was sunk into O. gramineum Willd.by Clausen (1938) who then, in July 1939, annotated Welwitsch's sheet of O. lusoafricanum in Kew as O. lancifolium Presl.In southern Africa, Schelpe (1970) and Schelpe & An thony (1986) have retained the epithet O. lancifolium for all species of Ophioglossum with a narrowly elliptic to lanceolate trophophore which is held clear of the ground on a distinct stipe.Recent studies have shown that there are three distinct taxa that display these general characters within south-central Africa.O. caroticaule (described above) appears to be rare.The most common species is a taxon with a rather variable trophophore shape and size but with two characters which clearly differentiate it from what is believed to be typical O. lancifolium: spore sculp turing (Figure 1A & B) and rhizome shape.This common taxon matches perfectly Welwitsch's O. lusoafricanum, a fact also recognized by Pichi Sermolli (1954) and Faden (1974).What is thought to be true O. lancifolium is re corded from central Africa but is not recorded from south of the 20°S line of latitude, being apparently confined to the Zambezian phytogeographical region (White 1983).
In his type description, Prantl (1884) quotes a specimen in Berlin as the type collection.Since all Berlin's Ophio glossum material was destroyed during World War 2, a neotype must be selected.
All the sheets seen of Welwitsch 34 in K and BM com prise more than one gathering.Although probably all of the same species, in a genus with species so poorly dif ferentiated as Ophioglossum, it is essential that a single gathering is selected as the type to avoid taxonomic am biguity.Therefore the top collection on the sheet in BM. composed of nine plants collected in January 1857, is hereby selected as the neotype of O. lusoafricanum.
O. lusoafricanum displays a confusing trait whereby the first emerging trophophore from a root sucker is fre quently ovate to orbicular and appressed to the ground, thereby resembling O. convexum J. E. Burrows.These small, ovate forms may sometimes produce fertile spikes, giving the impression that there are two topopatric species.However the spore pattern of the two species is quite dif ferent (Figure 2C, F, I, L) with O. convexum being con sistently trilete and O. lusoafricanum being alete or trilete.or rarely monolete.The spore sculpturing of O. convexum is variable which may indicate hybrid activity in some forms.
O. lancifolium is a name that has been widely applied to any species of Ophioglossum in tropical Africa that bears a narrow trophophore well clear of the ground (Schelpe 1970;Tardieu-Blot 1953;Jacobsen 1983).Al though plants which roughly correspond to Thouars' plants have been collected in central Africa, the status of O. lancifolium cannot be verified on the African mainland until good topotypic material is located from Mauritius.The extant specimens in Paris collected by Du Petit-Thouars from Mauritius are extremely poor and inade quate for a sound comparison.Specimens from mainland Africa share the same trophophore shape, the same rhi zome form and (possibly) the same spore ornamentation (Figure 2G, H).However it is vital that live plants are seen and collected from Mauritius before the African taxon can be equated with the type of O. lancifolium.Unfortunately Lorence, in his survey of the pteridophytes of Mauritius (1978), records against O. lancifolium: 'not seen recently'.
The distribution of the African taxon currently attrib utable to O. lancifolium: Angola, Namibia, Botswana, Zambia, Zimbabwe.

O.
latifolium most closely resembles O. rubellum Welw.ex A. Br.(with which it is most frequently con fused) but differs in its much larger size, its more slender rhizome with wider-spreading proliferous roots, the lack of orange pigmentation in the pedicel and trophophore, and its completely different spore ornamentation.
Up to now we have thought that this taxon could be a hybrid since three spore samples examined have all had malformed or undeveloped spores.This fact is also noted by Prantl in his original description where he states 'sporae degenerae'.However, apparently normal spores have been found in some collections which, together with this species' wide distribution, suggests that it is probably a stabilised hybrid with a very low percentage of viable spores produced.This is borne out by the populations seen being extremely localised and of obvious clonal origin.Nonetheless, there is no reason not to consider it a good species.
There seems to be no valid reason to assume that O. latifolium is allied to O. gomezianum since it shares very few characters with the latter species.Most noticeably, it lacks the suborbicular or ellipsoid rhizome that is typical o f O. gomezianum, whereas its consistently broader trophophores which are held almost flat on the ground, clearly separate it from O. gomezianum, and the taxon is therefore elevated to species level.
Although no holotype was designated by Prantl in his description.Schelpe (1977) illegitimately quotes the Kew collection as the holotype.The Kew sheet comprises two collections and the right-hand collection on the Kew; sheet is hereby selected as the lectotype of the name O. latifol-ium.Ballard's determination of that collection as O. costatum is incorrect.
In contrast, all the spores of the southern African taxon examined have a relatively uniform and fine reticulum which, in profile, is smooth (Figure 2J.K), lacking the jagged reticulum of the northern hemisphere taxon.Spore size, however, does not differ greatly [southern Africa: (27-)33^45(-60) (im; Europe/Asia: (28-)34-40(^T7) |im] although the southern African material tends to be slightly larger.
Pocock. in her unpublished manuscript on southern Af rican Ophioglossum, describes the southern African ma terial of O. vulgatum as a subspecies of the typical material, based, as she puts it, 'largely upon geographical considerations'.This, in itself, is not sufficient grounds for taxonomic distinction; however, the additional infor mation now available on spore morphology supports this separation, and the southern African material (none of the specimens examined for spore pattern have shown any resemblance to the northern hemisphere subspecies) is now regarded as a separate subspecies.Spores of O. vul gatum from East Africa have not yet been examined.

Selected specimens examined
Note: specimens of which spores have been examined by SEM are marked with an asterisk *.
woodland or on open sheetrock on seasonally wet vege tation islands.It is a gregarious species and, in all popu lations so far seen in the field, grows with either O. lusoafricanum,O.gomezianum Welw.ex A. Br., O. rubellum Welw.ex A. Br. or O. costatum R. Br.
The epithet vulgatum has been generally applied to southern African species of Ophioglossum that are mor phologically very similar to the north temperate O. vul gatum L. During a recent study of the genus in Africa, numerous SEM photographs have been made of spores of the southern African taxon.which has revealed a striking difference in spore morphology between the northern and southern hemisphere taxa.The spore morphology of O. vulgatum has been well documented in Europe