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The grass genera of the world

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

Calderonella Soderstrom & Decker

Named for C.E. Calderón, Panamanian botanist.

Habit, vegetative morphology. Perennial; stoloniferous and caespitose. The flowering culms leafy (the uppermost leaf with a reduced blade). Culms 70 cm high; herbaceous; unbranched above. Pluricaespitose. Plants unarmed. Leaves not basally aggregated. Leaf blades lanceolate; broad; 10–15 mm wide; flat; pseudopetiolate; cross veined (abaxially). Ligule present; an unfringed membrane (brown, papery, abaxially pilose); 0.1–0.2 mm long. Contra-ligule present (a hair fringe).

Reproductive organization. Plants bisexual, all with bisexual spikelets (3–5 dimorphous florets, the lowermost one (or two) pistillate and maturing first, the remainder staminate); without hermaphrodite florets (unless the second floret is sometimes functionally hermaphrodite).

Inflorescence. Inflorescence a single raceme (3–5 cm long, with 6 or 7 spikelets on short pedicels, the raceme terminating a long, filiform peduncle); espatheate (but uppermost leaf modified); not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes solitary; persistent. Spikelets solitary; not secund; pedicellate (the pedicels 1–2 mm long).

Female-fertile spikelets. Spikelets 8 mm long; compressed laterally (the lowermost floret becoming gibbous at maturity, causing the spikelet to bend at right angles to the rachis and become triangular in appearance); falling with the glumes. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets.

Glumes two; relatively large (G1 about 6.5 mm long, G2 about 4.5–5 mm); dorsiventral to the rachis; hairy (sparsely papillose-pilose intercostally); pointed; very dissimilar (G1 lanceolate, G2 parabolical in side view, both with transverse veinlets). Lower glume 13–16 nerved. Upper glume 10–11 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets clearly specialised and modified in form (i.e., they are male). Spikelets with proximal incomplete florets (lowest floret female-only).

Female-fertile florets 1 (the basal, which has 3 staminodes - but the second floret may have a (?)non-functional gynoecium). Lemmas with transverse veinlets; awnless; hairy (sparsely papillose-pilose between the veins); 15–19 nerved (but many nerves manifest only at base). Palea present; awnless, without apical setae (truncate, the apex ciliolate); 2-nerved (with a connecting transverse nervelet at the summit); 2-keeled. Palea keels winged. Lodicules present; 2; joined (the inner edges partially fused below, in front of the ovary); fleshy; heavily vascularized. Stamens 3 (staminodal - 3 in male florets their anthers non-penicillate). Ovary apically glabrous. Styles fused. Stigmas 2.

Fruit, embryo and seedling. Fruit small (about 2.3 mm long); compressed laterally, ventrally and at the base. Hilum short. Embryo small.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals narrower, more regularly rectangular, the walls less sinuous); of similar wall thickness costally and intercostally (quite thick walled). Mid-intercostal long-cells rectangular and fusiform; having markedly sinuous walls. Microhairs present; panicoid-type; 42–48 microns long; 4.5–6 microns wide at the septum. Microhair total length/width at septum 7–10.7. Microhair apical cells 27–30 microns long. Microhair apical cell/total length ratio 0.63–0.67. Stomata common; 27–33 microns long. Subsidiaries dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; silicified. Intercostal silica bodies cross-shaped. Prickles common. Crown cells absent. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; cross shaped, butterfly shaped, and dumb-bell shaped.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with adaxial palisade; without arm cells; with fusoids. The fusoids an integral part of the PBS. Midrib conspicuous (via its large bundle with a heavy I-girder combination, and what appears to be a double PBS of irregularly shaped cells); with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (large, wide groups, extending halfway into the mesophyll). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with the large bundles - the rest having abaxial girders but adaxial strands); forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Classification. Watson & Dallwitz (1994): Centothecoideae; Centotheceae. Soreng et al. (2015): Panicoideae; Zeugiteae. 1 species.

Distribution, phytogeography, ecology. Panama.

Shade species; glycophytic. Forests.

References, etc. Morphological/taxonomic: Soderstrom and Decker 1973. Leaf anatomical: this project.


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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: 13th November 2017. delta-intkey.com/grass’.

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