Merxmuellera Conert
Named for H. Merxmüller, German botanist.
Sometimes referred to Rytidosperma, Danthonia sensu lato
Habit, vegetative morphology. Perennial; caespitose. Culms 15–200 cm high; herbaceous; unbranched above; tuberous (in M. rufa, in the sense that the sheaths form a bulbous structure below the soil surface), or not tuberous. Culm nodes glabrous. Culm internodes solid, or hollow. Plants conspicuously armed (M. drakensbergensis having pungent leaf blades), or unarmed. Young shoots intravaginal. Leaves mostly basal (usually), or not basally aggregated (in M. arundinacea); non-auriculate. The mouths and bases of the sheaths often wooly. Leaf blades linear; broad (rarely), or narrow; 4–15 mm wide; nearly always rolled; disarticulating from the sheaths, or persistent (often disarticulating only when old); a fringe of hairs.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence a single raceme (rarely - M. disticha), or paniculate; contracted (narrow, occasionally spike-like, usually longer than 6 cm by contrast with Karroochloa); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets secund, or not secund; pedicellate.
Female-fertile spikelets. Spikelets 8–25 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairy (above); the rachilla extension with incomplete florets. Hairy callus present (0.6–2 mm long, with bearded margins). Callus short, or long.
Glumes two; more or less equal (G2 somewhat shorter); about equalling the spikelets to exceeding the spikelets; long relative to the adjacent lemmas; hairless; glabrous (shining); pointed; awnless; carinate; similar (papery, the margins and apex hyaline, the midnerve percurrent). Lower glume much exceeding the lowest lemma; 1 nerved, or 3(–5) nerved. Upper glume 1 nerved, or 3(–5) nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets without proximal incomplete florets.
Female-fertile florets 3–10. Lemmas similar in texture to the glumes; not becoming indurated; incised; 2 lobed; deeply cleft to not deeply cleft; awned. Awns 1, or 3; median, or median and lateral (the lobes sometimes finely awn-tipped); the median different in form from the laterals (when laterals present); from a sinus (the lobes sometimes basally adherent to it); geniculate; hairless; much longer than the body of the lemma. The lateral awns (when present) shorter than the median. Lemmas hairy, or hairless (rarely glabrous). The hairs when present, in tufts; not in transverse rows. Lemmas non-carinate (dorsally rounded); without a germination flap; (7–)9 nerved; with the nerves non-confluent. Palea present; relatively long (lanceolate); tightly clasped by the lemma; apically notched (bidentate); awnless, without apical setae; textured like the lemma; not indurated (hyaline); 2-nerved; 2-keeled. Palea keels wingless; hairy. Lodicules present; 2; free; membranous; ciliate (often), or glabrous. Stamens 3. Anthers without an apically prolonged connective. Ovary glabrous. Stigmas 2 (long, plumose); white.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small (2–3 mm long); not noticeably compressed.
Ovule, embryology. Micropyle oblique, or not noticeably oblique. Outer integument extensive, being absent only from the micropylar region, or covering no more than the chalazal half of the ovule; more than two cells thick at the micropylar margin, or two cells thick at the micropylar margin. Inner integument discontinuous distally; thickened around the micropyle, or not thickened around the micropyle. Synergids haustorial (weakly or strongly developed); exhibiting large, globular starch grains, or without large, globular starch grains (M. arundinacea).
Abaxial leaf blade epidermis. Costal/intercostal zonation lacking. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs absent. Stomata absent or very rare. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Costal short-cells predominantly paired. Costal silica bodies rounded and tall-and-narrow; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma. Leaf blade ‘nodular’ in section; with the ribs very irregular in sizes. Midrib not readily distinguishable (apart from its position); with one bundle only. Bulliforms not present in discrete, regular adaxial groups. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming ‘figures’ (anchors). Sclerenchyma not all bundle-associated (the anchors abaxially linked forming a continuous subepidermal band). The ‘extra’ sclerenchyma in a continuous abaxial layer.
Special diagnostic feature. Female-fertile lemmas with a bent awn, the awn twisted below. Spikelets 8–25 mm long, inflorescence longer than 60 mm long.
Cytology. Chromosome base number, x = 6. 2n = 12. 2 ploid.
Taxonomy. Arundinoideae; Danthonieae.
Distribution, ecology, phytogeography. 16 species; South and South West Africa. Mesophytic to xerophytic (often in mountains); species of open habitats; glycophytic.
Paleotropical and Cape. African. Sudano-Angolan and Namib-Karoo. South Tropical African.
References, etc. Morphological/taxonomic: Conert 1970, 1971. Leaf anatomical: Ellis 1981.
Special comments. Fruit data wanting.
Illustrations. • General aspect
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘Grass Genera of the World: Descriptions, Illustrations, Identification, and Information Retrieval; including Synonyms, Morphology, Anatomy, Physiology, Phytochemistry, Cytology, Classification, Pathogens, World and Local Distribution, and References.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).
