The blade of the culm sheath is a modified leaf. Its shape, whether it has hairs on the back or around the base, whether it is erect or bent backwards (reflexed), and whether it falls off early (deciduous), or will remain attached (persistent), are also all important.
Culm sheaths at the culm base are different from those higher up. They are broader and have shorter blades. To standardise descriptions, culm sheaths at eye-level on the large bamboos are collected and described. These are approximately ¼ of the way up the culm. Smaller bamboos are treated in the same manner, with culm sheaths from ¼ of the way up the culm from the base being described.
New culm sheaths show the features of the species best, but they usually only grow in the summer. Important parts of older sheaths are often missing. They may have fallen off, or rotted away, especially in hotter areas. For this reason bamboos are easiest to identify in the summer and autumn. In spring great care must be taken to find undamaged culm sheaths. Leaf sheaths are also damaged by strong wind and rain so that auricles, bristles, and hairs are blown off after a few months. New leaves can be found at most times of year except in mid-winter. Some of these should be collected as well as larger, older leaves. The drawings in this guide show fairly new parts. These are typical of those found from October to February.
The surface of the culm is also important. Young culms have a coating of wax, which can be either thick and furry, or thin, and either light or dark in colour. It may rub off quickly to leave the culms shiny, or it may persist so that the culms stay matt and dull. The joints of the culm (nodes) may be raised or level, with rings of wax, and they may bear small aerial roots or thorns. The surface of the culm may be rough with tiny sharp points, or smooth, or it may be covered in small vertical ridges.
Branching is a useful and important characteristic in bamboos, especially in the separation of genera. The number of branches in the first year of growth is most important, as well as the eventual number of branches that older culms develop. Whether these branches are all the same size should be noted, or whether the central branch is much larger than all the others, in which case it may develop aerial roots on its base.
Rhizomes are difficult to examine, but the type of rhizome will determine whether the bamboo grows in a clump or spreads widely. Spreading rhizomes may have roots at all nodes, or they may have roots only on the short internodes near the base of the culm, and they may be solid or hollow.
Flowers of bamboos are occasionally found. There are two different kinds of bamboo inflorescence. One type will keep on branching to give dense clusters or spherical balls of flowers, which are well-developed in tropical genera Dendrocalamus and Bambusa, and in Cephalostachyum. The other type produces flowers in panicles, similar to those of an ordinary grass. The panicles and flowers of Thamnocalamus remain partially hidden by sheaths, while the sheaths fall quickly from the panicles of other genera such as Drepanostachyum and Borinda.
The colour of the flowers can allow quick identification of the large bamboos if the flowers are young, but they will all fade to a brown or straw colour. Dendrocalamus hamiltonii var. hamiltonii has purple flowers with distinctive red anthers, while var. edulis has yellow flowers. Dendrocalamus hookeri has olive-green to brown flowers. Bambusa tulda and B. nutans have green flowers, while Bambusa balcooa has green flowers with purple tips. Bambusa clavata has large purple flowers with yellow anthers. Dendrocalamus giganteus has very long pendulous sprays of flowers.
To allow accurate identification of bamboos in the herbarium, a collection of leaves and culm sheaths is usually adequate if they are in good condition and well protected. The leaves can be packed inside a rolled culm sheath, and a series of culm sheaths can be rolled together and tied firmly. The outer sheaths will protect the delicate parts of those at the centre, such as the auricles and blades. For the small bamboos a section of the culm is very useful, including a node with its branches cut back to 5cm. For spreading bamboos a short section of the rhizome is also required. This can often be found on an overhanging bank or road cutting. If flowers are collected, leaves and culm sheaths should always be searched for and included, even if old. Collections should never be put in plastic bags as they will rapidly go mouldy. Bamboo culm sheath hairs can irritate. Contact with skin or food should be avoided