| # The grass genera of the world |

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

### Merostachys Spreng.

Including Brasilocalamus Nakai

Habit, vegetative morphology. Arborescent, shrubby or scrambling perennial. The flowering culms leafy. Culms woody and persistent; scandent, or not scandent; branched above. Buds from which the primary culm branches arise (where recorded) 1. Primary branches 11–20; around a triangular space. The branching dendroid. Culm leaf sheaths present (usually), or absent (M. fistulosa); deciduous; leaving a persisten girdle (rarely), or not leaving a persistent girdle; sometimes conspicuously auriculate (but mostly unknown). Culm leaves with conspicuous blades. Culm leaf blades linear, or lanceolate. Culm internodes solid, or hollow. Unicaespitose. Rhizomes pachymorph. Plants unarmed. Leaves with auricular setae. Leaf blades broad; pseudopetiolate; without cross venation; where recorded, disarticulating from the sheaths. Ligule an unfringed membrane. Contra-ligule present, or absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant, or all alike in sexuality; hermaphrodite, or hermaphrodite and male-only, or hermaphrodite and sterile (with imperfect spikelets towards the tips of the racemes).

Inflorescence. Inflorescence a single spike, or a single raceme (spicate, pectinate, terminal on leafy twigs). Inflorescence axes not ending in spikelets (the tips excurrent, with rudimentary spikelets). Rachides flattened. Inflorescence spatheate (with ‘bracts’ subtending at least the lowest spikelets); not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes spikes, or ‘racemes’; solitary; persistent. Spikelets solitary (usually), or paired, or in triplets; secund; sessile to subsessile.

Female-fertile spikelets. Spikelets elliptic, or lanceolate, or ovate; compressed laterally to not noticeably compressed; disarticulating above the glumes; when more than one-floreted, disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets.

Glumes one per spikelet (the upper); shorter than the adjacent lemmas; hairy; pointed; non-carinate. Upper glume 1 nerved (in material seen). Spikelets with incomplete florets. The incomplete florets both distal and proximal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; sterile (but sometimes with a rudimentary floret - hence its interpretation as an L1 rather than a G2). The proximal lemmas awnless; 3 nerved; similar in texture to the female-fertile lemmas (fragile, brittle); not becoming indurated.

Female-fertile florets 1–2(–10). Lemmas similar in texture to the glumes; not becoming indurated; awnless, or mucronate (?); hairy; non-carinate; without a germination flap; 9–11 nerved (in material seen). Palea present; relatively long; not convolute; entire; awnless, without apical setae; several nerved (6 in material seen); 2-keeled (and sulcate between). Lodicules present; 3; free; membranous; ciliate; heavily vascularized. Stamens 3. Ovary apically glabrous; without a conspicuous apical appendage. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; not noticeably compressed. Hilum with the hilum not visible externally. Pericarp thin, or thick and hard (leathery or crustaceous); fused, or loosely adherent. Embryo embryo not visible externally.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae present. Intercostal papillae over-arching the stomata; several per cell (mainly one row per long-cell, variable in size). Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls (thin). Microhairs present; panicoid-type (large, the basal cells variable in length); 45–54 microns long (in M. anceps); 9–12 microns wide at the septum. Microhair total length/width at septum 4.4–5.7. Microhair apical cells 24–28.5 microns long. Microhair apical cell/total length ratio 0.46–0.57. Stomata common (obscured); 27–30 microns long (in M. anceps). Guard-cells sunken, and obscured by papillae. Intercostal short-cells common; silicified. Intercostal silica bodies tall-and-narrow. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (mostly solitary, sometimes associated with large, bulbous prickles). Costal silica bodies present and well developed to poorly developed; tall-and-narrow.

Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with adaxial palisade; with arm cells (Metcalfe), or without arm cells (very inconspicuous in M. anceps); with fusoids. The fusoids external to the PBS. Leaf blade adaxially flat. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans, or associated with colourless mesophyll cells to form deeply-penetrating fans (if associated lignified cells are interpreted as ‘colourless cells’). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with most bundles); forming ‘figures’ (anchors with most bundles). Sclerenchyma not all bundle-associated. The ‘extra’ sclerenchyma in abaxial groups (opposite the bulliforms), or in adaxial groups (the ‘groups’ mostly reduced to one or few cells, in M. anceps); abaxial-hypodermal, the groups isolated and adaxial-hypodermal, contiguous with the bulliforms.

Classification. Watson & Dallwitz (1994): Bambusoideae; Bambusodae; Bambuseae. Soreng et al. (2015): Bambusoideae; Bambusodae; Bambuseae; Arthrostylidiinae. About 40 species.

Distribution, phytogeography, ecology. South America.

Forests.

References, etc. Leaf anatomical: Metcalfe 1960; studied by us - M. anceps.

Illustrations. • Merostachys speciosa: McClure, New World Bamboos (1973). • Merostachys petiolata, M. neesii, M. sparsiflora: Camus (1913). • Abbreviations for Camus (1913) figures. • Merostachys speciosa, M. ternata, M. aggronema: Camus (1913). • Merostachys claussenii: Nicora & Rúgolo de Agrasar (1987).

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: 15th June 2025. delta-intkey.com’.

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