Alpinia zerumbet

Alpinia zerumbet.

In Family Zingiberaceae, Shell ginger, native to S. E. Asia and China, is commonly grown as an ornamental.
It is becoming naturalised in S. E. Queensland.

Growing from rhizomes they can form clumps metres wide.
The pseudo stems are from 1 to 3 m high.
The alternately arranged leaves are in 2 ranks.

The leaf sheath is open.
The blunt topped ligule, up 1 cm long, has hairs on the outer surface and edge.
The oblong to lanceolate leaves are on petioles up to 1.5 cm long.
The blade can be up to 70 cm long and 15 cm wide.
The base is wedge-shape and the long narrow tip is twisted.
There are hairs, often dense, are on the edges near the tip.

Drooping terminal inflorescences, up to 30 to 40 cm long, are on a 1 to 2 cm long peduncle.
The dark reddish-purple midrib is densely hairy.
The developing flowers are protected by 2 large involucral bracts.
These fall off when the flowers open.

Each side branch has up to 2 or occasionally 3 flowers on stalks up to 2 cm long.
There are elliptic bracteoles around 3 cm long under each flower.
Sometimes deeply concave they resemble shells giving the plant its common name.
They are white with pink tips.

The 2.5 cm long white calyx has a basal tube with 3 pink-tipped lobes.
The tube is split on the lower side.
The shorter corolla tube has 3 oblong white lobes with pink tips.
The upper (dorsal) one is longer and wider than the lateral two.

The inner whorl of stamens has 1 fertile stamen and 2 staminodes.
    The stamen is around 2.5 cm long with a large anther.
    The 2 lateral staminodes are fused to form the labellum.
    This is ovate and up to 5 cm long and 4 cm wide.
    The curled in edges are wrinkled and the tip is notched.
    It is yellow with extensive dark reddish-purple lines.

In the outer stamen whorl one staminode is missing and the 2 dark red lateral ones are only a few mms long.

There are pale yellow nectiferous glands around the base of the style.

The inferior ovary has 3 locules each with numerous ovules.
It is covered in pale yellow hairs.
The 4 cm long style lies in front of the stamen filament then between the anther sacs.
The spherical stigma lies just above the anther.
The globular fruit are ribbed capsules that ripen from green to red.

Alpinia zerumbet ‘Variegata’ is a smaller plant with pale yellow stripes on the leaves.