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Branches

Branching patterns and characters Common branching patterns In-depth branching analysis Advanced branching characters Further information on branching systems in temperate bamboos is given in a draft publication

Woody bamboos have substantial development of culm branches. These vary considerably between genera, and so can be very useful for identification at the generic level, especially in temperate bamboos. Suitable material for inspection is required however, and full-sized living plants are generally required to make an accurate assessment. The characters can vary from node to node and over the life of the culm. Therefore to compare branching patterns of different bamboos the characters are standardised on the branches produced in the first year of branch growth from the mid-culm region of a culm from a mature clump.

Branching patterns and characters

Most bamboos produce a complement of several to many branches from each culm node. The simplest way to categorise these is by an inspection of a mid-culm node in the first year of branch growth. Branch growth forms can be sorted into the basic patterns given below, or it can be examined in depth to reveal a number of more detailed characters.   

Some common mid-culm 1st yr branching patterns:  

usually a single branch, eg Sasa, Pseudosasa japonica

unequal pairs, eg Phyllostachys

larger central and a variable series of 2 to 4 smaller laterals, eg Thamnocalamus, Bashania

larger central and consistently two smaller level basal laterals, eg Chimonobambusa, Sinobambusa

central with 2 to 6 laterals all subequal and more or less level, eg Fargesia, Yushania

7 to 100 or more subequal and more or less level or in several rows, eg Drepanostachyum, Chusquea

large central branch with 6-many subequal laterals surrounding it, eg Neomicrocalamus, Chusquea subgen Rettbergia

In-depth branching analysis

Close inspection of good material is required to analyse branching in depth. 

For bamboos to have several or many branches all originating close to the culm, the basal branch internodes have to remain very short, without intercalary growth. As extension of basal internodes is minimal on lateral branches as well as the central branch, the results after several years can be a highly complex complement of branches close to the culm, which can be difficult to examine, and may number several hundred branches.

The numbers of branches that are produced close to the culm depends upon the number of compressed basal internodes on the primary branch, how many of these have buds, and whether the resultant lateral branches have further compressed basal internodes and buds themselves. Which internodes have buds also varies, some bamboos having laterals on the most basal nodes, others having them further up the central branch.

In many bamboos the compression of basal internodes is so intense that several lateral second order branches are presented side by side, with a subequal primary branch in the centre. As the compression develops, the need for separating sheaths diminishes and sheaths on lateral branches may become completely absent. Thamnocalamus and Fargesia are quite similar alpine genera, but Thamnocalamus has retained all its sheaths, while Fargesia and several related genera have lost these sheaths, presenting several branch bases together. Other genera that often lack some of the sheaths in their complements of branches include Pleioblastus, Semiarundinaria, Chimonobambusa and Chusquea. The particular sheaths that are lost vary between these genera, suggesting the process has evolved independently. Cross-sections of the branch system are required to analyse and compare such patterns of reduction.

The time of growth of branching also varies. Some bamboos such as Phyllostachys have precocious branch development as soon as the culm internodes have elongated. Drepanostachyum, Himalayacalamus, and many S American bamboos also develop branches very quickly, and they are unusual in the bamboos in that the branches grow extravaginally, splitting open the culm sheath base. Other bamboos, such as Fargesia nitida produce culms one year, and branches only in the following year.

Branch development can vary substantially along the culm, buds at lower nodes often remaining dormant. Larger, central branches can remain dormant for many years, only the laterals growing from the outset. This has to involve two phases of lateral branch development, which is the normal procedure in tropical bamboos such as Bambusa. The central branch produces 2 lateral branches from 2 basal internodes, and often 2 branches grow from their basalmost internodes as well, and so on for higher orders of branching. These all grow simultaneously in the first year. A series of 1–4 buds distal to these remain dormant on the central branch and also on the laterals, and they only develop in the second year or later. Internodes without buds often separate the nodes from which the two phases of branching occur.

Dormant central branches are common in scrambling or heavily pendulous bamboos, eg Neomicrocalamus  and Dendrocalamus. If apical dominance is lost by the culm apex hanging out or down, or it being damaged, then the central branches can develop, sometimes growing nearly as large as the original culm. When central branches are very large, their bases can also be rhizomatous, eg in Dendrocalamus, and they can root if the culm falls down, giving these bamboos an alternative dispersal mechanism.

Advanced branching characters

  internodal compression on central branch base

                        no compression at all, eg Phyllostachys

                        variable compression of basal internode, eg Sarocalamus

                        basal internode consistently compressed, eg Pseudosasa japonica

                        several internodes compressed, eg Thamnocalamus

                        many internodes compressed, laterals arcuate not level, eg Rhipidocladum

                        several internodes compressed, laterals level, eg Fargesia

                       many internodes compressed, laterals level, eg Drepanostachyum, Chusquea

    presence of buds on compressed basal node

                        buds always present, eg Phyllostachys, Thamnocalamus

                        bud presence variable, eg Indocalamus tesellatus

                        bud usually absent on basal nodes, Sasa, Pseudosasa, Hibanobambusa

  sheathing reduction

                        all sheaths present, eg Phyllostachys

                        some sheaths occasionally absent, eg Semiarundinaria, Pleioblastus

                        several sheaths consistently absent, eg Yushania, Drepanostachyum

  time of central branch development

                        immediate, eg Phyllostachys

                        after dormancy, eg Fargesia nitida

  time of basal lateral branch development

                        one phase, eg Yushania

                        two phases, eg Bambusa                     

  manner of branch development

                        usually extravaginally, eg Drepanostachyum, Chusquea

                        infravaginally, eg Pseudosasa japonica, Pleioblastus

Further information on branching systems in temperate bamboos is given in a draft publication