The node on bamboo stems
I thought that the leaves on branches would be important for identifying bamboos. I was mostly wrong. Much more important are culms (main stems) and the sheaths on them.
Culms consist of nodes where buds and branches originate and internodes between them. In most bamboos, the internodes are cylindrical, uninterrupted, hollow cylinders. Between internodes are the nodes (https://www.inaturalist.org/observations/24976209). Branches originate at nodes (https://www.inaturalist.org/observations/188842578). Nodes are solid and have a couple of rings. The next paragraphs explain node architecture, staring at the bottom of the node.
The sheath scar is the place where the culm leaf sheath was attached. It is usually dark, differing in color, often protruding a bit (https://www.inaturalist.org/observations/193091108). Occasionally it involves two close-together, parallel lines (https://www.inaturalist.org/observations/193091108), depending on sheath thickness or how it detaches. The sheath scar may be horizontal (https://www.inaturalist.org/observations/24976209) or tilted ( https://www.inaturalist.org/observations/195794898 ).
The node itself is above the sheath scar. It starts within the sheath so is a bit narrower than the scar but becomes wider as it grows up, a slight inverted pyramid (https://www.inaturalist.org/observations/193091108, https://www.inaturalist.org/observations/195794898). Sometimes it's nearly cylindrical.
The supranodal (or nodal) ridge (or ring) is actually part of the node itself. It's a thickened ridge of tissue from which the branch buds may emerge. It is a shape, not be any line of tissue on the surface. Sometimes shading makes it obvious and sometimes there is also a difference in color https://www.inaturalist.org/observations/(https://www.inaturalist.org/observations/193091108). It may be exaggerated so it seem distorted, wider than the sheath scar (https://www.inaturalist.org/observations/189532708) or about equal to the sheath scar (https://www.inaturalist.org/observations/188401643) or in some species it's not present and the area is just a cylinder. The sheath scar and supernodal ring may be close together (https://www.inaturalist.org/observations/195794147) or farther apart (https://www.inaturalist.org/observations/193091108).
Branch number turns out to be more important than I ever would have guessed. Some species have one per node (https://www.inaturalist.org/observations/186581970), e.g. Pseudosasa and Pleioblastus. The common genus Phyllostachys is characterized by having 2 branches per node, sometimes with a third, smaller branch (https://www.inaturalist.org/observations/188842578). Some bamboos have several branches per node (e.g. Samiarundinaria fastuosa, https://www.inaturalist.org/observations/195794898, and Bashania fargesia, https://www.inaturalist.org/observations/193091108). In any species, the lower nodes often lack branches (https://www.inaturalist.org/observations/188401648).
I'll include a couple of internode traits that involve nodes. In that distinctive genus Phyllostachys, the internode is grooved from one node to the next, the groove originating just above a branch (https://www.inaturalist.org/observations/188842578, https://www.inaturalist.org/observations/195795204). Lower parts of culms often don't have branches, and if they don't, they lack grooves, too (https://www.inaturalist.org/observations/191824162); look higher up to find them. Leaf sheath often fall off the culm quickly; they're early deciduous (https://www.inaturalist.org/observations/191824162, e.g. on Phyllostachys) or they may be retained, sometimes for years (https://www.inaturalist.org/observations/197501761, e.g. for Pseudosasa). Sometimes they are tardily dehiscent; they detach on the sides but stay attached at the middle and often stay on for a year or so (https://www.inaturalist.org/observations/189532707, e.g. Bashania and Semiarundiaria.).
