Culms
Stems of grasses are called culms. Their unitary construction is obvious, with prominent nodes and internodes. Their form in terms of posture is an important character, linked to wall thickness and branch development. The production of erect culms with limited rhizome development from basal subterranean culm nodes is known as tillering. This is different from production of further pachymorph rhizome axes, and is found in bamboos with leptomorph or long-necked pachymorph rhizomes, giving a pluricaespitose clumping habit in both.
Internode length, diameter, and wall thickness can be consistent or it can vary greatly, and in certain cultivars it can be abnormally short. Details of swellings or grooves, indumentum (hairs, bristles and wax), and thorniness, are all important characters for distinguishing genera and species, and many different character states are possible.
Nodes and/or supra-nodal ridges may be raised, and a scar where the culm sheath is joined to the node may be adapted into a prominent corky disc, useful to semiscandent bamboos for support on tree branches, as are dense short retrorse spines on the internode surface. Between the scar, bearing the persistent remains of the base of the sheath, and the supra-nodal ridge is the area where aerial root initials form in some species, these being specialized into a ring of tough thorns in a few genera.
Many of these are very important characters to the horticulturalist, especially in cultivars in which stripes of different colours are present on the culms, or internodes are swollen or shortened.
Characters of culms
Posture
(self supporting)
erect, eg Semiarundinaria fastuosa
nodding, eg Phyllostachys
pendulous, eg Drepanostachyum
(supported)
semiscandent, eg Chusquea valdiviensis
climbing, eg Dinochloa
Tillering
rare, eg Phyllostachys edulis, Bambusa, Melocanna
common, eg Pleioblastus simonii, Yushania maling, Pseudostachyum
Internodes
wall thickness
internodes solid, eg Chusquea culeou
subsolid or very thick, eg Dendrocalamus strictus
thick, eg Bambusa vulgaris
thin, eg Dendrocalamus hookeri
very thin, eg Pseudostachyum polymorphum
length
consistent, eg most bamboos, Bambusa vulgaris
shortened internodes, eg Phyllostachys aurea
lengthened internodes, eg Arthrostylidium
compressed, swollen internodes, eg Bambusa ventricosa
surface (many character states possible, varying in time, some examples:)
uniformly white-pubescent at first, eg Oligostachyum
distally setose, eg Borinda papyrifera
proximally and distally persistently white-scurfy
uniformly lightly waxy at first, becoming glossy
distally densely scabrous, eg Yushania maling
covered with uniform glaucous wax, eg Himalayacalamus hookerianus
basal internodes with sparse, fine vertical lighter green stripes
cross-section
circular eg Fargesia
somewhat quadrangular eg Chimonobambusa quadrangularis
grooved above buds and branches (sulcate):
eg Phyllostachys, Chimonobambusa quadrangularis
Nodes
supranodal ridge
absent, eg Himalayacalamus planatus
raised, eg Semiarundinaria, Phyllostachys
prominently swollen, eg Chimonobambusa tumidissinoda
node
level, eg Himalayacalamus planatus, Borinda perlonga
slightly raised, eg Borinda frigidorum
raised, eg Fargesia denudata
a hard flange eg Neomicrocalamus
sheath scar (if sheath base fused to culm node)
very thin and level, eg Himalayacalamus planatus
a raised corky collar, eg Borinda contracta, Pleioblastus viridistriatus
a thick corky flange, eg Ampelocalamus patellaris, Ampelocalamus scandens
glabrous/initially pubescent/persistently pubescent
persistent sheath base (if separable from culm)
fragmentary, eg Thyrsostachys
substantial, eg Gigantochloa
well distinguished from sheath, a girdle:
short eg Neomicrocalamus, tall eg Melocalamus
glabrous/initially pubescent/persistently pubescent
aerial roots (usually only in basal half of culm)
absent, eg most temperate bamboos
initials present, eg Dendrocalamus hookeri
well developed, eg Dendrocalamus hamiltonii
adapted into ring of thorns, eg Chimonobambusa quadrangularis
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