Taxonomy and leaf anatomy of the genus Ehrharta (Poaceae) in southern Africa: the Dura group

The Dura species group in the genus Ehrharta Thunb. is differentiated morphologically by the perennial habit and the very large, awned, subglabrous spikelets and anatomically by the occurrence of tanniniferous cells and wax platelets obscuring the stomatal pores. The Dura group consists of two species, E. dura Nees ex Trin. and E. microlaena Nees ex Trin., which occur only in Mountain Fynbos. The group shows no clear morphological or anatomical relationship with other species groups in the genus in southern Africa. Die Dura-spesiegroep in die genus Ehrharta Thunb. word morfologies deur die meerjarige groeiwyse en die besonder groot, genaalde, ylbehaarde blompakkies onderskei en anatomies deur die aanwesigheid van tannien-selle en wasplaatjies wat die huidmondjieporiee verberg. Die Dura-groep bestaan uit twee spesies, £1 dura Nees ex Trin. en E. microlaena Nees ex Trin., wat slegs in Bergfynbos voorkom. Die groep vertoon geen duidelike morfologiese of anatomiese verwantskap met ander spesiegroepe in die genus in suidelike Afrika nie.


E. microlaena is easily distinguished from all other
Ehrharta species by the perennial habit,the large,glabrous, long-awned spikelets and the setaceous leaf blades.It is hydrophytic, and grows on streamsides and in damp peaty places in Mountain Fynbos.Like E. dura.most of the specimens seen were collected after fire.However, the distribution of E. microlaena is more restricted than that of E. dura, extending from the Kogelberg Forest Reserve north through Paarl, Bain's Kloof, Du Toit's Kloof and Ceres to Tulbagh (Figure 3) at altitudes of 400 to 1 330 m.There is little intraspecific variation, and specimens from throughout the range are similar in appearance.Flowering occurs from December to February.

1.
LEAF ANATOMY O F E. DU RA

Transverse section
The leaf blade is open and expanded (Figure 4A) but has the ability to inroll from the margins under adverse moisture conditions.The midrib is not structurally dis tinguishable from the lateral first order vascular bundles and is not associated with colourless parenchyma.Suc cessive first order bundles are separated by three smaller bundles, usually two third order bundles with a single second order bundle between them (Figure 4A) although this pattern is not always consistent (Figure 4B).Well developed, rounded to slightly flattened adaxial ribs are located over all the vascular bundles (Figure 4A -C).These ribs generally are all the same size but the smallest third order bundles may be associated with smaller ribs (Figure 4B).The furrows between adjacent ribs are deep, narrow and steep-sided and tend to become cleft-like with leaf inrolling.Conspicuous bulliform cells occur at the bottom of these furrows (Figure 4C).
The mesophyll tissue is irregularly arranged.The chlorenchyma cells are larger than the bundle sheath cells, angular and fitting tightly together with the chloroplasts concentrated around the cell circumference (Figure 4C).The walls are straight with no arm cell-like invaginations.No large intercellular air spaces are visible.Colourless parenchyma is absent between the bundles although colourless adaxial bundle sheath extensions are associated with the smaller bundles (Figure 4B, C).The vascular bundles are surrounded by two bundle sheaths, an outer sheath of many (up to 26) small colourless cells and a distinct mestome sheath of cells with uniformly thicken ed secondary walls (Figure 4C).All the epidermal cells contain conspicuous, dark, resin-like deposits distributed evenly across the entire width of the blade (Figure 4B  C).

Abaxial epidermis
Costal and intercostal zones are differentiated (Figure 4D, E).The intercostal long cells are rectangular with slightly wavy anticlinal walls (Figure 4D, E) and inflated outer walls (Figure 5A -C ).All contain black tanninife rous deposits generally filling the entire cell lumen (Figure 4E).Adjacent long cells in a f ile are separated by single or paired shon cells (Figure 4D, E).Cell size and arrange ment is uniform across each intercostal zone.
Stomata occur in a single file on either side of each intercostal zone, immediately adjacent to the costal zones (Figure 4E).Successive stomata are separated by single interstomatals and neither the subsidiary cells nor the interstomatals contain tanniniferous deposits.The subsidiary cells are low dome-shaped and not sunken below the general level of the epidermis (Figure 5C, D).The stomatal pores are obscured by dense accumulations of wax platelets (Figure 5D).4D, E).Micro hairs were not observed with the light microscope but are clearly visible with the SEM (Figure 5C, E).These hairs have a short basal cell with a blunt distal cell (Figure 5E).Small pointed, single-celled intercostal macrohairs are very rare (Figure 5F).

Abaxial epidermis
Herbarium leaf blade material was used to prepare abaxial epidermal scrapes of this species.The epidermal structure is very similar to that of E. dura, and reference should be made to the description above.Both species have the diagnostic tanniniferous intercostal long cells which dominate the epidermis and are unique to this species group in Ehrharta.

Transverse section
No fresh leaf blade material of this taxon was avail able for anatomical study, and consequently the transectional anatomy was not examined.Engelbrecht (1956) has shown that the leaf blade is cylindrical in section with the interior containing colourless parenchyma tissue.This structure appears to result from the fusion of the two margins and not from a reduction of the lamina on either side o f the midrib with the resultant blade being only a rounded keel.This specialized blade needs detailed anatomical study as it represents an interesting adaptation within the genus.tendency towards semi-radiate chlorenchyma with abaxial palisade-like cells in the Villosa group (Ellis 1987).The Setacea (Ellis 1987) and Ramosa groups and the Longifolia subgroup all lack keels but differ from the Dura group in many other respects (Gibbs Russell & Ellis 1987).
The abaxial epidermis is differentiated into costal and intercostal zones with rectangular long cells, low dome shaped subsidiary cells, irregularly dumbbell-shaped silica bodies, prickles with short barbs and microhairs with blunt distal cells.Epicuticular wax is absent except in association with the stomatal apertures where wax platelets obscure the pores.This combination of epider mal attributes is distinctive and serves to distinguish the Dura group from the others (Gibbs Russell & Ellis 1987).Rectangular long cells are shared with the Villosa and Ramosa groups but the stom ata, silica bodies and micro hairs differ between these three groups.
The unique tanniniferous epidermal cells found in the species o f the Dura group are of great interest because these represent the only known C3 grasses which possess this type of cell (Ellis in prep.).No bambusoids, pooids or other arundinoids are known to have this type of epidermal cell which is also rare in the chloridoids and panicoids, except the Andropogoneae and Arundinelleae, where many species and genera exhibit tanniniferous cells.The colour and texture o f the contents of the epidermal cells of E. dura and E. microlaena are con sistent with that of the tanniniferous cells observed in these C4 grass taxa and it is presumed that they contain the same chemical substance.All 90 South African grass species in which this type of cell has been observed are unpalatable species from oligotrophic soils and it is in ferred that these cellular contents are polyphenols which function as a chemical defence against herbivores (Ellis in prep.).Their presence in the Dura group may repre sent a separate and similar adaptation to which no phy logenetic importance should be attached.
The anatomical observations of this study generally agree with previous reports but for a minor exception.Tateoka (1963) described the subsidiary cells of E. dura as being almost parallel-sided, whereas here they are shown to be low dome-shaped.However, the distinction between these two stomatal types is only slight and a difference in interpretation may have resulted in this apparent inconsistency.The work o f Engelbrecht (1956) is in full agreement with this study.
It is of interest that in one o f the five specimens of E. dura examined by Engelbrecht (1956) a distinct keel, incorporating five vascular bundles with extensive adaxial parenchyma, was observed.This appears to be an inter mediate condition between E. dura and the cylindrical blade of E. microlaena.It appears as if the cylindrical leaf blade of E. microlaena represents an adaptation to hygrophilous habitats and the intermediate specimen probably came from a damp locality.Unfortunately it is not possible to deduce which specimen displayed this anatomy from the work of Engelbrecht (1956).Never theless, this represents the first possible intermediate between these two species which are otherwise so clearly separated anatomically and morphologically.
E. dura and E. microlaena are undoubtedly closely related to each other, yet have very little in common with any other species of Ehrharta in southern Africa.Both spikelet morphology and leaf anatomy indicate that they occupy an isolated position within the genus and are not linked to any of the other species groups.The two taxa are treated at the level of species because they are differentiated by both vegetative and spikelet characteristics, have very different transectional leaf blade anatomy and their habitats are somewhat different.In addition, although the two taxa occur sympatrically.they flower at different times and no morphologically intermediate specimens have been observed.

1 .
. The Dura group is a small, apparently isolated group composed o f only two species, E. dura Nees ex Trin.and E. microlaena Nees ex Trin.The two species are distinguished morphologically from other Ehrharta species by correlation o f perennial habit, large spikelets 9 -1 7 mm long and awned sterile lemmas with glabrous sides, keel and margins.The spikelet plan of the Dura group is shown in Figure 1.Anatomically the Dura group is distinguished within Ehrharta by the presence of tanniniferous cells and by wax platelets obscuring the stomatal pores.The spikelets and leaves of the species have a characteristic olive-green colour that is distinctive and may result from the dark tannins in the intercostal long cells of the epidermis.The species differ from each other principally in awn length and in leaf blade shape and width.Both species occur only in Mountain Fynbos.The two species in the group present no nomenclatural difficulties because they were described by Trinius (1839) in the same publication, and other authors have consis tently followed this treatment (Nees 1841; Steudel 1853; Stapf 1900; Chippindall 1955); thus neither species has synonyms.The same treatment is followed here.This singularly simple situation is undoubtedly a reflection o f the distinctness of the Dura group within Ehrharta and the unusually low degree of intraspecific variation present.It is more difficult to assess to what degree the simplicity of treatment also results from the infrequent collection of the species due to their restrict-Ehrharta dura Nees ex Trin. in Phalaridea, Me mories de l'Academie imperial des Sciences de St-Petersburg, ser.6, 5: 13 (of reprint) (1839); Nees: 218 (1841); Steudel: 5 (1853); Stapf: 665 (1900); Chippindall: 37 (1955); Smook & Gibbs Russell: 55 (1985).Type: Drege, Du Toit's Kloof, 3 000 ft, (LE!, lecto., here de signated; K!,P!).Perennial, erect, forming large leafy tufts, rarely longrhizomatous.Rhizomes woody, with glabrous, thickened cataphylls.Culms several to many, to 800 mm long, 4 mm across, herbaceous, crowded, unbranched, hollow.Young shoots intravaginal.Leaves mostly basal, culm leaves with blades well developed, sheaths not overlap ping; leaves auriculate, auricles produced from top of sheath; basal sheaths flabellate and slightly twisted, tight, persistent, hard, reddish brown, bearing blades; ligule a membrane fringed with hairs or sometimes near ly glabrous, 1 ,5 -3 ,0 mm long; leaf blades persistent, erect, herbaceous, glabrous, lanceolate, 4 -10 mm across, flat or folded, becoming rolled from margins when dry; blade bases folded, thickening with age, persistent and conspicuous often even in burned plants; blade tips gradually tapering.Inflorescence a panicle, open, 7 0 -2 0 0 mm long, considerably overtopping leaves; main axis straight, often closely subtended or enveloped below by uppermost leaf sheath; numerous spikelets, spikelets appressed to the axes and held nearly erect but somewhat secund.Spikelets pedicellate, distinctly compressed laterally, 9-16 mm long, 3 mm across laterally (above glumes), olive-green.Rhachilla prolonged beyond fertile floret.Glumes not keeled, the lower V, or more the length o f the upper, V 4 -V2 as long as spikelet, white, or green, appressed to lemmas at maturity.
, tufted, apparently lacking long rhi zomes.Culms several, to 1 100 mm long, 2,5 mm across, herbaceous, crowded, unbranched, hollow.Young shoots intravaginal.Leaves mostly basal, culm leaves with blades reduced, sheaths not overlapping.Leaves auriculate, the auricles produced from the base of the blade and adnate to the margins of the ligule.Basal sheaths somewhat flabellate, tight, eventually deciduous, membranous, light brown, or whitish, bearing blades.Ligule a glabrous

Florets with lemmas decidedly firmer than the glumes, keeled. Sterile lemmas laterally compressed, sides flat, similar in shape, texture and ornamentation; with keel and margins parallel; base not stipitate, without auriculate appendages, shortly bearded, sides scabrous or sometimes with short hairs, dull, with 3 -1 1 strong or fairly distinct longitudi nal ribs; tip tapering gradually from body of lemma to an arista or awn. Awn 2 -1 6 mm long. First sterile lem ma about V 2 to 2/s length of second sterile lemma. Fer tile floret shorter than second sterile lemma. Lemma of fertile floret differing from sterile lemmas, strongly laterally compressed and sides unomamented, faintly 3-5-nerved, sides glabrous, tip truncate with a tuft of minute hairs. Palea thinner than lemma, 3/4 or more as long as lemma, keeled, 1-nerved. Lodicules 2, membra nous, 2-lobed, margins ciliate. Stamens 4 or 6. Anthers 7 mm long, yellow. Ovary glabrous. Stigmas white. Caryopsis 9 mm long, laterally flattened. E. dura is distinguished from southern African Ehr harta species in other groups by the perennial habit and the large nearly glabrous mucronate to awned spikelets. It is distinguished from closely related E. microlaena by the broad leaves and the broad, brown, flabellate bases. It grows in mesophytic to seasonally moist open habitats in Mountain Fynbos in sandy or loam soils over sand stone or granite at altitudes of 430 to 1 300 m. A single specimen (Boucher 2028) came from an altitude of 30 m at Kogelberg State Forest. All but a few of the speci mens seen were collected after a bum. E. dura extends along mountain ranges from Stellenbosch and Worcester to Humansdorp (Figure 2), and has a much wider distri bution than E. microlaena. Most Ehrharta species show considerable variation in habit and leaf development, and it is possible to recognize ecotypes and local variants. In contrast to this common pattern, E. dura is remark ably constant in its appearance from the eastern to the western ends of its range, with no geographically corre lated infraspecific variation. Flowering occurs from September to December.
Vouchers: A c o c ks 22817; B ond 1611; Taylor 4211, 10256; Z eyher 4513.Bothalia 18,2 (1988) FIG URE 2. -D istribution o f E. dura.