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