Leaf anatomy of the South African Danthonieae (Poaceae). Pentameris dregeana

Transverse sections and abaxial epidermal scrapes of leaf blades of Pentameris dregeana Stapf, both of herbar­ ium specimens and of freshly fixed material, were examined by light microscopy. The anatomical structure was found to be basically uniform in a representative sample. A few somewhat atypical specimens, how'ever, showed epidermal similarities with Pentaschistis colorata (Steud.) Stapf. A comparison with other danthonoid grasses re­ vealed some specimens identified as Pentaschistis colorata var. polytricha Stapf which resemble Pentameris dre­ geana very closely in leaf anatomy. A definite gradation in leaf anatomy between Pentameris dregeana and Penta­ schistis colorata appears to exist and. consequently, it is proposed that the affinities of Pentameris dregeana lie with this group of Pentaschistis species rather than close to any of the other Pentameris species.


INTRODUCTION
Pentameris dregeana Stapf is a densely tufted per ennial which is usually not as robust as the other members of this genus. The leaf blades are tightly inrolled and wiry, and the old leaves are characteris tically curly. Soft, woolly hairs are particularly com mon on the leaf sheath but may also occur near the base of the blade. The inflorescence is a panicle with rather small spikelets, the glumes being from 12-15 mm long (Chippindall 1955). The spikelets are therefore smaller than in any of the other species of Pentameris. where the glumes range from 18-25 mm long.
Pentameris dregeana is a species of the mountain fynbos, and is confined to the mountains of the south-western Cape Province, where it occurs from the Clanwilliam District in the north-west to Willowmore in the east. It favours rocky habitats and is of ten found in rock crevices or cliff faces. The species is even found at high altitudes in the alpine zone but it does not form low, dense cushions with pungent leaf apices as does P. macrocalycina (Steud.) Schw-eick.
Apart from the statement by De Wet (1956) that both the epidermal and internal anatomy are festucoid. no information on the leaf anatomy of P. dre geana is available. It is the purpose of this paper to describe and illustrate the leaf anatomy of P. dre geana in detail and to compare its structure with that of the other species of the genus as well as the other South African danthonoid grasses. For the anatom ical descriptions, the terminology of Ellis (1976Ellis ( . 1979 will be followed and the following abbrevia tions will be used: vb/s -vascular bundle/s l 'vb/s -first order vascular bundle/s 3'vb/s -third order vascular bundle/s ibs -inner bundle sheath; mestome sheath obs -outer bundle sheath; parenchyma sheath

Leaf in transverse section
Outline of lamina: inrolled from both margins; probably never open and expanded: not permanent ly infolded type but margins usually almost meet, forming an enclosed, hollow cylinder (Figures 1-9). 11, 13. 15 or 17 vbs in blade section. Ribs and fur rows: flat-topped, square adaxial ribs present over all vbs; deep, cleft-like furrows between all vbs (Fig  ure 6); ribs over l'vbs and 3'vbs of similar shape and size. No abaxial ribs or furrows although slight undu lations may be associated with the vbs (Figures 3 &  4). Median vascular bundle: structurally identical to lateral l 'vbs; recognizable by location only. Vascular bundle arrangement: 5. 7 or 9 l'vbs in leaf section; 1 3'vb separates successive l 'vbs ( Figures 1-9), al though laterally this pattern may be obscured. No 2'vbs. All vbs located in centre of blade thickness ( Figure 9) or slightly abaxially ( Figure 6). Vascular bundle description: 3'vbs elliptical with well devel oped phloem, l'vbs elliptical with phloem adjoining the ibs; metaxylem vessels narrow, narrower in di ameter than the obs cells ( Figure 6). Vascular bundle sheaths: obs elliptical; interrupted both adaxially and abaxially by bundle sheath extensions intergrading into sclerenchyma girders (Figures 6 & 9). Obs cells small, rounded, with thin walls and no chloroplasts. Ibs entire; composed of rounded cells with thicker inner tangential cell walls. Sclerenchyma: all vbs with prominent adaxial and abaxial girders; narrow towards bundles; girders either intergrade with thick-walled collenchyma of bundle sheath exten sions ( Figure 6) or sclerenchyma fibres abut on the ibs abaxially and the obs adaxially ( Figure 9). Very small sclerenchyma cap in margin ( Figure 9). Mesophyll: homogeneous chlorenchyma consisting of regular, tightly packed, isodiametric cells, not ra diate ( (Figures 14-17); unicellular, soft, thin-walled and 1-2 mm long; base slightly swollen, superficially located between several modi fied epidermal cells. Not of cushion hair type. Costal zones: 5-7 files wide. Long cells of similar length to intercostal long cells but much narrower; each long cell separated by a silico-suberose couple consisting of a crescentic cork cell and a round to elliptical sil ica cell.

DISCUSSION A N D CONCLUSIONS
The 14 examined specimens of Pentameris dregeana were collected at localities throughout the dis * Specimens have abaxial macrohairs. tribution area of the species. Yet their leaf anatomy is remarkably uniform, and both the leaf in trans verse section (Figures 1-9) and the abaxial epidermis (Figures 10-17) show negligible variation. This is considered unusual seeing that ecotypical variation is common in many fynbos species in response to the diversity of habitats in this ecologically varied re gion.
A superficially striking difference, however, is the presence of conspicuous, long, soft macrohairs on some of the specimens of P. dregeana studied (Fig  ures 14-17). Although this appears to be a signifi cant difference, it must be remembered that all specimens of P. dregeana have this type of macro hair on the leaf sheath, particularly at the sheath mouth (Chippindall 1955). These hairs are possibly also present on the leaf blades of all P. dregeana specimens but normally confined to those parts of the blade below the central third which was sampled in this study. In the pubescent specimens examined, this type of hair merely extends somewhat higher up the leaf blade than is normal. In addition, the leaf transections of these pubescent specimens ( Figures  7-9) are identical to those of the typical specimens (Figures 1-6). No taxonomic significance is there fore. attached to the presence or absence of these hairs, although pubescent leaf blades were found al most exclusively in specimens from the eastern parts of the distribution area of P. dregeana. This mav. however, represent clinal variation.
A less obvious difference is. that on some epider mal preparations costal and intercostal zones are not differentiated (Figures 10-11). On others this zonation is clearly distinguishable by differences in cell structure and arrangement (Figures 12-17). The in tercostal long cells are rectangular with wavy anticli nal walls and the cells of a file are all separated by small, narrow short cells. The long cells of the costal zones are much narrower and the interspaced silica bodies are of the same width as the long cells.
Although the leaf anatomy of P. dregeana is con sistently uniform and stable, a few specimens identi fied as P. dregeana deviate from the typical structure to varying degrees (Figures 18-24). In transverse section these atypical specimens display typical P. dregeana anatomy (Figures 18-20) but the epidermal structure differs somewhat. The differences are not discrete, however, and a continuum exists from those specimens where the costal and intercostal zones are almost indistinguishable to the situation in Figure 24 (Ellis 2477) where costal and intercostal long cells are significantly different. This particular specimen also differs from all others in that the silica bodies are dumbbell-shaped and microhairs occur between the intercostal long cells (Figure 24). In transverse section this anomalous specimen is indis tinguishable from typical P. dregeana specimens (Figures 18 & 19). and it is of interest to note that it was collected at the same locality on the Gvdoberg as Ellis 2480. which has typical P. dregeana anatomy (Figures 1 &. 13).
These atypical specimens, and Ellis 2477 in par ticular. seem to indicate a link between Pentameris dregeana and Pentaschistis colorata (Steud.) Stapf ( Figures 25-32). This possible relationship is not evi dent in leaf transections, because Pentaschistis colo rata and its close allies have very characteristic abaxial epidermal cells between the bundles alternating with small, fibrous cells overlying the bundles. Nevertheless, relationships of P. dregeana appear to lie with this group of Pentaschistis species rather than with any of the other Pentameris species. All these 'atypical' P. dregeana specimens should un doubtedly be retained in P. dregeana on gross mor phological features and have been artificially separ ated here only to accentuate the anatomical link be tween P. dregeana and Pentaschistis colorata.
The following P. dregeana specimens display aty pical leaf anatomy to varying degrees: The anatomical gradation of Pentameris dregeana into the Pentaschistis colorata species complex ap pears to be substantiated by the observation that some specimens identified as Pentaschistis colorata (Steud.) Stapf var. polytricha Stapf are virtually identical to P. dregeana in leaf anatomy e.g. Ellis 2347, 2509 (Figures 25-28). (Figures 29-30), collected at the same locality as Ellis 2509 (Figures 27-28), has a leaf anat omy very closely resembling that of a specimen iden tified as Pentaschistis aristidoides (Thunb.) Stapf (Ellis 2488 to that of both Pentameris dregeana and Pentaschistis colorata, and this example demonstrates the definite interface between Pentameris dregeana and the genus Pentaschistis. It is clear that the affinities of Pentameris dregeana are closer to some species cur rently placed in Pentaschistis than they are to any of the Pentameris species.

Ellis 2506
Ellis 2546 (Figures 31-32) is another specimen identified as Pentaschistis colorata var. polytricha, but its leaf anatomy differs from that of all other danthonoid grasses known to the author. Further collections of this taxon are needed before it can be positively identified, but indications are that this specimen represents a new and undescribed species, possibly belonging to Pentameris. It is mentioned here because it emphasizes the extreme heterogene ity of Pentaschistis colorata var. polytricha. a taxon which presently accommodates some specimens matching Pentameris dregeana as well as specimens which resemble neither P. dregeana nor Pentaschistis colorata. Pentaschistis colorata var. polytricha is therefore a heterogeneous entity which appears to substantiate the anatomical indications found in this study, namely that Pentameris dregeana grades into Pentaschistis and shows closer affinities to this genus than it does to any other Pentameris species.
The following specimens examined during this study w'ere identified as Pentaschistis colorata var. polytricha by the staff of the National Herbarium: Pentameris dregeana resembles some of these specimens linked to Pentaschistis colorata more than it does the other species of Pentameris such as P. longiglumis (Nees) Stapf (Ellis 1985a), P. thuarii Beauv. (Ellis 1985b), P. macrocalycina (Steud.) Schweick. (Ellis 1985c) and P. obtusifolia (Hochst.) Schweick. (Ellis 1985c). The anatomical affinities of P. dregeana are undoubtedly closer to Pentaschistis colorata and its allies than to the other members of the genus Pentameris. It's leaf anatomy appears to be somewhat intermediate between these two gen era and a final decision on the classification of this interesting species awaits a thorough revision and reevaluation of the genus Pentaschistis.