Poaceae – bamboos


Family Poaceae has 115 genera with over 1700 species in 3 sub-families.
Subfamily Bambusoideae is divided into 3 tribes:
    Arundinarieae with nearly 600 species of temperate woody bamboos in 33 genera,
    Bambuseae has nearly 1000 species of tropical woody bamboos in 75 genera and
    Olyreae has 130 species of herbaceous bamboos in 20 genera.

Generalised features of bamboos.

Bamboos can be divided into two groups based on their rhizomes and growth habit.

Monopodial bamboos have rhizomes with a permanent terminal growing point.
These can grow rapidly and extend 3 m or more in the first year.
The rhizomes are thinner than the culms and each of the more widely spaced nodes can produce
    roots and a new culm resulting in a potentially invasive running bamboo.

In contrast the sympodial or clumping bamboos have rhizomes that lack a single persistent growing point
    at the tip with growth transferred to successive lateral buds.
The shorter, slow growing rhizomes are thicker than the culms and each produces only one culm in addition to roots.
Over time the root mass just gradually increases.
The culms are usually close together forming a dense clump but in some species the new culms are up to 1 m apart giving a loose clump.

The culms, (stems or canes) with the culm sheaths, arise from the underground stems or rhizomes.
New culms reach their full height within a year.
They grow rapidly with the fastest increasing by 0.3 m or more in 24 hours.
The height varies from under a few cms up to 20 or 30 m with those commonly seen being between 1 to 15 m.
Culm diameter ranges from 0.5 up to 20 cm.

Culms are mainly erect but can also be erect with drooping tips, arching or rarely pendulous.
A few climb by twining and others scramble when the weight of the top of the culm becomes too much to support.
They are solid at the nodes but most are hollow in between.
Nodes can be swollen or oblique, have short hairs and the lower ones often have aerial roots.

The internodes may be the same length along the whole culm or shorter (compressed) at the base and to a lesser extent at the top.
Some species have a broad groove above the nodes that can run the full length of the internode or just the lower part of it.
The internodes may be angled giving a zigzag appearance or they can be swollen.
There may be a prominent ridge above the node and young culms may have fine hairs on the internodes.

Many culms are green, yellow or black but they can be cream, white or brown.
They may have green, yellow, silvery or black stripes of various widths and some have blotches instead of stripes.
Some have a white, powdery bloom all over or just under the node.

Bamboos have protective &/or supportive sheaths (modified leaves) at the nodes in three areas:
    rhizome sheaths or bracts, lying tightly along the rhizome, are permanent.
    culm sheaths, from the culm nodes, usually fall off when the side branches and their leaves have grown.
    leaf sheaths (sometimes called foliage leaves) protect the developing leaves and tend to remain.
They consist of the sheath with a blade attached to the upper edge.

Culm sheaths.
The young upper sheaths are mostly green and leaf-like but some are bluish or yellowish.

The older ones at the base are dried out and brown.
The upper margin may be straight or curved upwards in the centre.
The outer surface can be plain or striped and young sheaths have thin or thick hairs
    that can be black, brown, white or yellowish.
The inner surface is smooth and shiny.
The blade has dark hairs on the inner surface but none externally.

On the upper inner margin of the sheath, behind where the blade attaches is the ligule which lies tightly against the culm.
This can be a row of hairs or a small membrane a few mms high that may have teeth &/or hairs on the margin.
The auricles are small or prominent projections at the top of the sheath on either side of the ligule.
They may have thicker and longer hairs (bristles or setae) on the upper margin.

On the outer surface of the sheath, corresponding in position to the ligule, there may be an external ligule or callus.
This consists of two very small to prominent raised flaps that may be smooth or have short hairs.

Culm features are important in identifying bamboos and those around a quarter of the way up the culm
    should be examined or those at eye level in tall bamboos.

Side branches and leaves.
These can appear before or after the culms attain their full height.
Branches are alternate and the number from each node varies with the species ranging from 1 to many.
One or two branches are often larger than the others and are said to be dominant.

The branches are tree-like with each branchlet having from 3 up to nearly 20 leaves.
The alternately arranged leaves are typically lanceolate with the end tapering to a point.
Some have more ovate leaves while a few species have fine, fern-like leaves.
The base of the blade commonly narrows into a short pseudopetiole which may twist or bend.
Blade size varies from 5 to 30 cm in length and 1 to 5 cm or so wide.

There may be hairs on the lower blade surface and the pseudopetiole.
The blade edge usually feels rough due to small hard spines.
There may be longer setae or bristles on the edge near the base.
Some have prominent cross veins between the parallel ones giving the blade a tessellated appearance.
Blades are various shades of green with some having cream, yellow or green stripes.

Leaf sheath.
The open leaf sheath, with or without hairs, fits tightly against the culm.
At the inner junction of the blade and sheath is the ligule with a flat, toothed or eroded top.

There may be auricles with setae and an external ligule as in the culm sheaths.

Flowers and fruit.
Some species never flower while most take years or decades to do so.
Some flower but do not produce seed.
The spikelets have basal glumes and a mix of small fertile and sterile florets.
Fertile florets have a palea and lemma, up to 3 lodicules, 3 or 6 stamens and a superior ovary with 1 to 3 stigmas.
(These structures are described in detail in the section on grasses.)
They reproduce mainly by new shoots from the rhizomes.

For parks, gardens etc. bamboos are chosen for their growth habit (size, density of foliage,
    speed of growth, clumping or running, degree of branching, etc.) and colours.
Australian nurseries stock at least 12 Bambusa, 9 Dendrocalamus, 8 Gigantochloa,
    7 Schizostachyum species plus 16 others most of which are clumping types.
Also available are nearly 30 varieties and cultivars some of which are very similar.