Systematic studies in the genus Mohria ( Pteridophyta : Anemiaceae ) . VL Taxonomic review

A taxonomic review o f the genus Mohria Sw. is presented, including diagnostic features, distribution and variation. A key to the taxa in the genus is provided and each species described.


INTRODUCTION
The genus Mohria Sw. is largely an African one, occurring from the Western Cape in South Africa, along the eastern mountain ranges as far north as Kenya.Al though the genus has a largely eastern distribution, two species, M. lepigera (Baker) Baker and M. vestita Baker, also occur on the Bihe Plateau in southern Angola.Moh ria, furthermore, tx'curs on Madagascar and Reunion Is land.
Mohria was first described by Plukenet ( 17(X)) as Filicula geranii arvensis folio et facie aethiopica.It was not until 1771 that Linnaeus in his Mantissa plantarum altera de scribed Polypodium caffmrum from a Konig collection.Konig, a pupil of Linnaeus, was on his way to Tranquebar (India) but spent a short period (April 1-28, 1768) at the Cape of Gtxxl Hope, where he collected on Lion's Head, Table Mountain, Devil's Peak, the Hals towards Constantia and along the sea shores (Gunn & Ctxld 1981).
The younger Linnaeus, however, in his Supplementum plantarum (1781), transferred Polypodium caffrorum L. to the genus Adiantum L. P. caffrorum has since been trans ferred to genera such as Lonchitis L. by Bemhardi (1801) and Colina by Greene (1893).Before describing the genus Mohria in 1806, Olaf Swartz initially placed what is today known as Mohria caffrorum in the genus Osmunda L. (Swartz 1801).At the time of publication of the genus Mohria, M. thurifraga was the only species known.
The genus Mohria honours Daniel Matthias Mohr, German botanist and later professor of philosophy at the University of Kiel (Stafleu & Cowan 1981).
A review of the genus has never been undertaken, with the result that all the collections, till recently, have either been placed in M. caffrorum or M. lepigera.The review presented here is the result of studies on the morphology and anatomy of the rhizome and frond (Roux et al. 1992), vestiture morphology (Roux 1992a), sporangium and spore morphology (Roux 1992b) and karyology (Roux 1994).

Diagnostic featu res
Mohria lepigera is characterized by its generally long and narrow frond outline, the short stipe in relation to the lamina length (x = 1:10; n = 30), the often greatly reduced and widely spaced proximal pinnae and the large, densely set stramineous to cream-coloured sinuous-walled scales which often cover the entire abaxial pinna surface.Clavate trichomes are 30.5-(42.52)-48.8pm long and naviculate trichomes are 50.0-(113.44)-147.5|im long.

Distribution and habitat
Mohria lepigera occurs in Tanzania, Burundi, Zaire, Malawi, Mozambique, Zimbabwe and Madagascar (Fig ure 2).M. lepigera occurs from 1 200-2 400 m in habitats ranging from rock crevices or boulder bases and riverine fringes to moist open ground.Komas (1979) dealt with the ecology of the taxon in Zambia.

Variation
Mohria lepigera shows a fair amount of plasticity in the degree to which the Jamina is divided, lamina size, texture and indumentum composition and density.Collec tions recorded from moist shaded conditions at higher elevations have relatively short, less dissected (2-pinnatifid) membranous fronds, whereas those from xeric environments have relatively long, 2-pinnate, firmly her baceous fronds which are borne in an erect manner.The densely scaled abaxial surface which is typical of M. lepigera in some instances only bears filiform scales and hairs.

2.
Mohria marginalis (Savigny) J.P Roux in South African Journal of Botany 56: 401 ( 1990b).c, E, G, i, k,   Bory has always been considered as the author of Osmunda thurifraga (Schelpe 1970(Schelpe . 1977;;Schelpe & An thony 1986) but the name was published without a description.Bory (1804: 348) merely noted "Dans les en virons je trouvai une belle fougere, dont les feuilles froissees repandaient l'odeur de l'encens: je 1'ai vue depuis dans l'herbier de M. de Jussieu, elle lui venait de Commerson, qui l'avait appelee Osmunda thurifraga.'It is therefore evident that he did not describe, nor had any intention to describe, the species, as in other parts of this work he either provided a short description or gave a ref erence to a previous work where he thought a taxon to be new.The name is therefore a nomen nudum.
Savigny (1798) also published Commerson's manu script name Osmunda thurifraga as a nomen nudum.citing it as one of the elements used in his description of O. marginalis, the other being a Sonnerat collection from Reunion.The Commerson specimen in the herbarium of the Museum National d'Histoire Naturelle.Paris (P) was designated as the lectotype of O. marginalis Savigny (Roux 1990b).Desvaux (1811), in his description of Mohria crenata, gave the locality of the species as "Habitat in insula Bourboniae' (Reunion), with no collector given.The specimen designated here as lectotype of M. crenata is a sheet which formerly formed part of Desvaux's herbarium and is currently housed in the herbarium of the Museum National d'Histoire Naturelle, Paris (P).

Distribution and habitat
Mohria marginalis occurs from the southern Drakens berg in the northeastern Cape along the mountain ranges into central Africa, as far north as Burundi.It also occurs on Reunion (Figure 2).In the Drakensberg the taxon oc curs in seasonally moist, often exposed situations at the rim of vegetation pockets commonly found in shallow depressions in the Clarens Sandstone formation, at boulder bases or among grass tussocks at higher elevations.Fur ther north it has been recorded from rock crevices.The plants usually form large masses and may often grow alongside xerophytic ferns such as Cheilanthes eckloniana (Kunze) Mett., Ophioglossum lancifolium C. Presl and M. rigida J.P. Roux.

Variation
Slight variations occur in frond length, the number of segments per pinna and in the indumentum density on the stipe and rachis.Narrow hair-like scales often replace some of the hairs on the abaxial lamina surface.

3.
Mohria caffrorum (L.) Desv. in Memoirs dc la Societe Linneenne de Paris 6. 2: 198 (1827) 1806) is a superfluous name for Polypodium caffrorum L. (1771).However, the con cept of this species as construed by Swartz (1806) includes two different elements, namely a Cape taxon and a Reunion taxon.The latter was described as Osmunda mar ginalis Savigny based on collections by Commerson and Sonnerat from Reunion and is here upheld as a distinct species.
The description and illustration published by Lowe (I860) is that of M. vestita (No. 6).Here he mentions a dwarf form of this species which was known as M. achilleifolia.This he described as M. thurifraga var.achil leifolia in 1862.A Sim collection annotated by him as M. thurifraga var.achilleifolia from Zwaartberg near Pieter maritzburg, Natal, is housed in Pretoria (PRE) but this proved to be a variant of M. vestita.However, the illustra tion (t.62B) provided by Lowe which is based on a Sim collection, judging by the size and laminar segmentation, appears to be a collection of M. caffrorum.The collection has obviously not been preserved and I therefore designate plate 62B as iconotype of M. thurifraga var.achilleifolia.

Diagnostic features
Mohria caffrorum is characterized by the branched, often widely creeping stoloniferous rhizome, the marked degree of dimorphism in the fertile frond stipe which is strikingly longer than the sterile frond stipe, indumentum structure and distribution, and spore ornamentation.Clavate trichomes are 55.0-(59.15)-67.5 (am long and naviculate trichomes are 147.5-(179.8)-222.5 (im long.

Distribution and habitat
Mohria caffrorum is found in the Northern, Western and Eastern Cape where it occurs in a wide range of ecological and climatic conditions (Figure 4).It grows at elevations ranging from almost sea level at Cape Point to ± 1 000 m in the Cedarberg.Plants are generally found in small clonal clusters at boulder bases, in rock crevices or in light shade of shrubs, or in large stands in seasonally moist exposed situations.Fires, which are prevalent in most of the vegetation types in which the species occurs, appear to have no ill effect on the plants but rather stimu late them.

Variation
Scale density and scale outline or structure on the abaxial lamina surface show the most striking degree of variation.When scale variation throughout the distribution is viewed, a gradation in scale outline is detected from the west, becoming more complex to the east.Scale varia tion is especially apparent in the Gifberg/Vanrhynsdorp ecotype where the abaxial surface of the mature fronds of some plants is densely covered by large pale brown to whitish scales with sinuate-walled cells (Figure 3J-0).
M. caffrorum shows the highest degree of frond dimor phism.The difference between stipe length of the sterile and fertile fronds is the most significant.A relationship exists between frond and stipe length in the sterile frond (r = 0.724, P <0.001) and the fertile frond (r = 0.530, P < 0.001).Fertile fronds proved to have a larger number of pinnae and pinnules than sterile fronds.

Diagnostic featu res
Mohria saxatilis is distinguished by the short prostrate rhizome, short stipe, the crowded fronds, the large spread ing scales on the stipe and on the abaxial lamina surfaces, and the broadly winged costa.Diagnostic micromorphological characters are the larger clavate trichomes which are 61.1-(68.11)-76.4Jim long (Roux 1992a), and epidermal cells and the occurrence of copolocytic and tripolocytic stomata not found in any of the other taxa (Roux et al. 1992).Naviculate trichomes are 97.7-(139.05)-177.19(im long.

Distribution and habitat
Mohria saxatilis is confined to the Table Mountain Sandstone formation and occurs from the Cedarberg to the Langeberg in the Worcester District.The species grows at elevations ranging from ± 1 000 to 1 500 m (Figure 4).

Distribution and habitat
Mohria rigida is restricted to elevations of 1 800-2 438 m along the Drakensberg, the adjacent mountainous Lesotho and the Transvaal Highveld and escarpment (Fig ure 4).In the Drakensberg the plants usually occur in dividually or in small groups consisting of a few plants in the alpine and subalpine vegetation belts as defined by Killick (1963).Almost without exception they occur in seasonally moist, often exposed, rock crevices.

Variation
Variation occurs in frond and pinna length and in the density, size and outline of the scales on the abaxial and adaxial lamina surfaces.In Mohria rigida the stipe/lamina ratio ranges from 1: 0.84 to 1: 7.0 (jc = 2.45; n = 45).

Diagnostic featu res
Mohria vestita is characterized by the short stipe/ lamina ratio, the reduction in size of the pinnae towards the lamina base, ossiform-celled hairs which adaxially are confined to the secondary rachis and veins, and the rela tively small, generally hastate and sparsely set twisted scales which are also confined to the secondary rachis and veins on the abaxial surface.Clavate trichomes are 30.0-(51.31)-63.4 |xm long and naviculate trichomes are 85.0-(138.32)-196.54|im long.

Distribution and habitat
The distribution of Mohria vestita ranges from the southern Cape along the central mountain ranges as far north as Kenya.It also occurs on the higher lying areas of Angola and in Madagascar (Figure 7).M. vestita grows in habitats ranging from coastal subtropical con ditions to elevations exceeding 3 000 m along the Natal Drakensberg.On Mount Kilimanjaro, M. vestita has been recorded at elevations ranging from 1 200-1 400 m and at Humpata in Angola it occurs at 2 220 m.Fires are common throughout the distribution area of M. ves tita, but appear to have no effect on the subterranean rhizome.

Variation
Variation in frond length can be ascribed to the wide distribution and diverse environmental conditions throughout the range.In hostile environments the fronds may be merely 109 mm long but al lower, more favourable conditions the fronds may measure up to 690 mm.Irrespective of variation in frond length, a relation ship exists between stipe and frond length in the sterile (r = 0.683, P <0.001) and fertile (r = 0.711, P <0.001) fronds.Variation in the density and distribution of in dumentum is most apparent.Hairs on the adaxial and abaxial lamina surfaces appear to increase as the distribu tion extends to the north.Slight variation in the cell struc ture may also be evident.
Mohria nudiiLSCula was recently described by Burrows & Burrows in Burrows (1989) as M. caffmrum var.ferruginea.Unaware of this study.I described the same species as M. nudiuscula (Roux 1990a).However, when my manuscript was in press, M. caffrorum (L.) Desv.var.ferruginea J.E. Burrows & S.M. Burrows was published.Although the latter name antedates M. nudiuscula I found it to be a distinct taxon and believe it not to be related to M. caf frorum.In accordance with Article 11.2 of the Interna tional Code of Botanical Nomenclature (1994) the name M. nudiuscula is adopted.

Diagnostic features
Diagnostic features in Mohria nudiuscula are the thick, coriaceous texture of the lamina, the often less dissected lamina, the shallowly crenulate or obtuse teeth and the almost glabrous adaxial lamina surface (hence the specific epithet).In most cases, however, a few long hairs, or small scales, may occur adaxially along the secondary rachis; abaxially long filiform scales also occur along the veins on the stipe and rachis.Diagnostic micromorphological characters are the absence of stomata from the adaxial lamina surface, the presence of pericytic and paracytic stomata and the cuticular ridges occurring adaxially along the major veins (Roux et al. 1992).Clavate trichomes are 37.0-(50.5)-62.5 |im long and naviculate trichomes are 120.8-(156.4)-190.2|im long.

Distribution and habitat
Mohria nudiuscula is largely confined to higher eleva tions with the distribution ranging from the Amatola Mountains in the Eastern Cape, along the KwaZulu-Natal Drakensberg, where this species has been recorded at elevations up to 2 400 m. and along the escarpment be tween the northeastern Orange Free State and KwaZulu-Natal.It is also widespread throughout the higher parts of Lesotho.Further north it occurs along the mountain ranges between Zimbabwe and Mozambique at elevations ranging up to 2 545 m. the Nyika Plateau in Malawi and the adjacent Rungwe Mountain range in Tanzania.In Zim babwe, M. nudiuscula also occurs on serpentine-derived soils along the Great Dyke and as far west as the Victoria Falls (Figure 2).The habitat is subject to frequent bums which is evident from the fire scars borne by some col lections.

Variation
When material throughout the distribution is viewed, an increase in frond length and pinna number becomes apparent towards the north.Fronds of plants occurring along the higher reaches of the Drakensberg are generally caespitose, firmly coriaceous and less dissected (2-pinnatifid) with the pinnae and pinnules crowded and over lapping.To the north, however, and especially along the mountains in eastern Zimbabwe, the fronds become erect and rigid.They are also more dissected (2-pinnate) with the pinnae and pinnules often distally spaced.The lamina texture along the northern limits of the distribution area also appears to be less coriaceous.