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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Gerritea Zuloaga & Morrone

Named for Gerrit Davidse, agrostologist.

Habit, vegetative morphology. Perennial; caespitose. Culms 20–100 cm high (procumbent, to 120 cm long); herbaceous; profusely branched above. The branching simple. Culms many. Culm nodes hidden by leaf sheaths; hairy (pilose, with long whitish hairs). Culm internodes hollow. Young shoots intravaginal. Leaves not basally aggregated (mostly cauline); minutely auriculate; without auricular setae. Strongly keeled. Leaf blades linear-lanceolate; broad to narrow; 7–15 mm wide; flat; pseudopetiolate (attenuate to a 2 cm long pseudopetiole); without cross venation; disarticulating from the sheaths. Ligule a fringed membrane (abaxially pilose); truncate; 0.3–0.6 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality; hermaphrodite.

Inflorescence. Inflorescence many spikeleted; paniculate (terminal, exserted, lax, pyramindal); open (14–30 cm long, 4–12 cm wide with divergent first-order branches, the peduncle up to 10 cm long); with capillary branchlets (?); espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelets solitary; not secund; long pedicellate (the pedicels flexuous, to 8 mm long).

Female-fertile spikelets. Spikelets 1.8–2.2 mm long (0.5 mm wide); elliptic; greenish or tinged with purple; slightly compressed laterally; falling with the glumes (?); disarticulating between the florets; with conventional internode spacings. The upper floret not stipitate. Rachilla terminated by a female-fertile floret. Hairy callus absent (?).

Glumes two; very unequal to more or less equal (subequal, or the lower somewhat shorter); long relative to the adjacent lemmas; hairy (with long, papillose-based hairs towards the margins); pointed (acuminate); awnless; non-carinate; very dissimilar to similar (the lower acuminate, the upper acute). Lower glume 0.75–1 times the length of the upper glume; longer than half length of lowest lemma; 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets more or less fully developed (0.7–1 mm long, hyaline, 2 nerved). The proximal incomplete florets sterile. The proximal lemmas glumiform, acute; awnless; more or less equalling the female-fertile lemmas, or decidedly exceeding the female-fertile lemmas (?); similar in texture to the female-fertile lemmas (?); not becoming indurated.

Female-fertile florets 1. Lemmas narrowly ellipsoid; similar in texture to the glumes (? - ‘membranous’); smooth; not becoming indurated; ‘pale’; entire; pointed; awnless; hairless; glabrous; non-carinate; having the margins lying flat on the palea; 3 nerved. Palea present; relatively long; gaping (free of the lemma at the tip); awnless, without apical setae; not indurated; 2-nerved. Palea back glabrous. Lodicules present; 2; free; fleshy (‘truncate’); glabrous; not or scarcely vascularized. Stamens 3. Anthers 0.6–0.7 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2; white (‘whitish’).

Fruit, embryo and seedling. Disseminule unknown.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Intercostal zones with typical long-cells. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; panicoid-type (the distal cells sharply pointed); 70–98 microns long. Stomata common; 26–32.5 microns long. Subsidiaries non-papillate; triangular. Intercostal short-cells common (irregularly dispersed); in cork/silica-cell pairs and not paired (solitary and paired); silicified. Intercostal silica bodies cross-shaped (or irregular). Small hooks and macrohairs present. Costal short-cells conspicuously in long rows. Costal silica bodies present and well developed; ‘panicoid-type’; dumb-bell shaped.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with radiate chlorenchyma; more or less Isachne-type. Leaf blade slightly ‘nodular’ in section; with the ribs more or less constant in size (low round topped). Midrib conspicuous (by the large median bundle and keel); with one bundle only, or having a conventional arc of bundles (sometimes with two small laterals). The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups (in each furrow); in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming ‘figures’ (anchors). Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paspaleae; Paspalinae. 1 species (G. pseudopetiolata).

Distribution, phytogeography, ecology. La Paz, Bolivia.

Mesophytic; shade species; glycophytic.

References, etc. Morphological/taxonomic: Zuloaga and Morrone 1993. Leaf anatomical: Zuloaga and Morrone 1993.

Special comments. Fruit data wanting.

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The 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. Version: 11th December 2017.’.