Download free Adobe Acrobat PDF Reader

Inflorescences

Inflorescence structure Characters

Inflorescence structure

Bamboo inflorescences vary greatly in overall form, and in the finer details of the individual spikelets and florets that they contain. They are categorized according to their density, extent of branching, presence of bracts, and position on the plant. As in all grasses the actual flowers, if any real parallel to the standard concept of a flower exists at all, are very small and inconspicuous. They are sessile (stalkless) and largely hidden inside 2 bracts, looking like the beak of a bird, which can open to allow pollination. These bracts are a prophyll, the palea, and a surrounding sheath, the lemma. Inside them, a ring of 3 tiny membranous bracts, the lodicules, is thought by some to represent the petals. Inside them are the ovary and stamens. The flower combined with its palea and lemma, is called a floret.

The florets are themselves sessile on alternating sides of a stalk, the rhachilla, and one to many florets are combined into a small spike, the spikelet. Descriptions of spikelet and particularly floret details are generally the same as those for other grasses. As the floret is so small with basic bracts, there being little or no adaptation for animal-related seed dispersal in bamboos, there are few characters for description. The number of characters found on the other sheaths, the culm sheath and the foliage leaves, along with the culm and rhizome, is much greater. That is one reason why grass taxonomists, who are trained to classify grasses mainly from the flowers, tend to lump many bamboo species together, not to mention the genera as well. Fleshy fruits are found in some bamboo genera, while most have a small dry caryopsis.

Historically, the bamboo inflorescence has received less critical scientific study than the inflorescences of other grasses, because of the infrequency of flowering and also the scarcity of bamboo plants in the western world. This is unfortunate as the unitary construction of the bamboo plant, and the evident homologies between vegetative and floral structures, provide insights into ontogeny, homology and phylogeny largely unavailable in other grasses.

It has been appreciated that certain bamboo inflorescences have structures that are not found in other grasses, and that the spikelets can develop in a different manner. There is often an ability for the spikelet to branch from basal buds and thus produce further spikelets. This, along with the presence of bracts on inflorescence branches, is sometimes assumed to be ancestral, and sometimes assumed to be derived. Four characters are involved, presence of buds in the spikelet, growth of those buds, presence of subtending bracts in the inflorescence, and presence of prophylls in the inflorescence.

It has been suggested that 2 categories of inflorescence, called semelauctant and iterauctant can be defined, and that the spikelets of the iterauctant inflorescence should be called pseudospikelets, though not by this implying that they are not homologous with spikelets in the semelauctant inflorescence. However, these 4 characters are not always well correlated, and which of the 4 characters should be used as the criterion for placing an inflorescence in one group or the other has not been agreed. Moreover, spikelets and pseudospikelets are clearly homologous. Therefore it is arguable that the terms semelauctant, iterauctant, and pseudospikelet have become confused and misleading, and are probably best avoided altogether.

Detailed inflorescence structure, including an analysis following the topologies and terminology of Troll and colleagues, has been considered elsewhere, and covered in depth in Stapleton (1997). It is interpreted as a modification of a simple polytelic synflorescence. The florescence is a component of the spikelet, with a zone of inhibition representing the glumes. Lateral paraclades with coflorescences together with the main florescence constitute the synflorescence. Following this critical analysis, which would make the constituent parts of the grass inflorescence homologous with inflorescences in other families, there are problems of conflicting usage of terminology, for example there can be no panicle or pedicel, as grass panicles and pedicels are not homologous with panicles and pedicels in other families. The substantial revision of terminology thus required means that it is not likely to be adopted for the foreseeable future in grass circles, and a more traditional usage of terminology is followed here.

Further Reference Stapleton, C. M. A. (1997). The morphology of woody bamboos. In G. P.  Chapman, (ed.), The Bamboos: 251–267. Academic Press.

Characters of bamboo inflorescences

  Inflorescence branch structure

  inflorescence prophyll

                        narrow, 1-keeled, eg Dendrocalamus

                        broad, 2-keeled, eg Bambusa

  branch bracteation

           prophylls

                        prophyll at point of branching eg Bambusa, Neomicrocalamus

                        prophyll distant from point of branching (rare, eg Racemobambos)

                        absent eg Arundinaria

 other sheaths

                        fully bracteate, eg Bambusa, Phyllostachys

                        partially bracteate, some substantial bracts remaining, eg Fargesia

                        mainly ebracteate, bracts all severely reduced to absent eg Arundinaria

  branching extent

                        racemose, strictly 1 order of branching, eg Fargesia

                        racemose-paniculate, 1 to 2 orders of branching, eg Thamnocalamus

                        paniculate, 2 or more orders, eg Dendrocalamus, Gaoligongshania

  density

                        capitate, many orders of branching, eg Dendrocalamus

                        spicate, few orders of branching, eg Bambusa

                        compressed, eg Fargesia, Thamnocalamus, Himalayacalamus

                        open, eg Yushania, Drepanostachyum

  grouping

                        fascicled, eg Drepanostachyum

                        not fascicled, eg Yushania

  branch orientation

                        unilateral, eg Fargesia,

                        not unilateral, eg Dendrocalamus

  branching angles

                        branches becoming deflexed, axils pulvinate, eg Gelidocalamus

                        branches remaining erect, axils not pulvinate, eg Pseudosasa

  surface

                        glabrous, eg Drepanostachyum

                        pubescent, eg Bashania

                        angles scabrous, eg

Spikelets

 position

                        sessile, eg Phyllostachys

                        borne on promontory, ‘pedicellate’, eg Yushania

  ramification

   basal bracts (glumes) with buds

                        buds developing (infl. iterauctant, spikelets often called pseudospikelets), eg Bambusa

                        buds not developing (inflorescence semelauctant), eg Thamnocalamus

   basal bracts with or without buds present, some developing, eg Chimonobambusa

   basal bracts without buds, eg Drepanostachyum

 glumes (sterile lemmas)

                         number gemmiferous, number empty, size

  number of florets

  termination

                         complete floret, incomplete floret, rhachilla extension

  rhachilla

                         internode length, pubescence

                         disarticulation

Floret (standard description as used in other grasses)

  fertile lemma: pubescence, marginal ciliation, apex

  palea: pubescence, marginal ciliation, keels, keel ciliation, apical division, apex

  lodicules: number, shape, fimbriation

  ovary: shape, pubescence

  stigma: length, division, stigma number and shape

  stamens: number, filament separation, anther length, anther apices

  fruit: dry caryopsis vs fleshy fruit, shape, size, length of beak (persistent stylar base)