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Sesbania cannabina (Retz.) Pers. 1807
pronounced: sez-BAN-ee-uh kan-nuh-BIN-uh
(Fabaceae – the pea family)
subfamily: Faboideae – the bean subfamily
common name: Sesbania Pea
This plant is found in central and northern regions of Australia. It is a common and highly competitive weed in cotton-growing areas, particularly on cultivated fields, channels, and other wet areas. The plant photographed was in a vacant block of land in Nelly Bay. There is another in Picnic Bay, growing in the bed of Butler Creek, near the Picnic Street crossing. There are also a number of plants on the verges of the West Point Road. Once Sesbania Pea has reached over 50 cm high, it is difficult to control, especially when it is growing among the plants of the cotton crop. It grows very rapidly, and, if unmanaged, the stems of the plant can become so thick that they need to be cut with an axe before the field can be picked. Heavy infestations can prevent the cotton crop from being harvested. As seeds are not produced until fairly late in the season, timely control will prevent seed dispersal.
With the seedlings, the cotyledons are oblong in shape, 1–2.5 cm long and 5 mm wide, borne on a very short stalk. The first true leaf has an elongated oval shape about 1.7 cm long, also borne on a very short stalk. The second true leaf has 5 pairs of leaflets. The number of leaflets increases on later leaves. The young stems and leaves often have spreading hairs. The mature leaves are 5–20 cm long and made up of a number of oblong, mostly hairy, pairs of leaflets, often 12–30 pairs, but sometimes up to 45. Each leaflet is 5–20 mm long and 1.5–4 mm wide, and has a small point on the rounded leaflet tip.
The plants are erect, 1–3.5 m tall. The stems are green or reddish purple in colour and much branched, generally on the upper stem.
The flowers are pea-like and yellow to yellow-orange, 10–15 mm long, with dark-purplish streaks or spots on the back. The flowers occur in the leaf-stalks singly, or in groups of up to 6, on stalks 5–40 mm long.
The seed-head is a long cylindrical pod, 12–20 cm long and 2.5–4 mm wide, slender and drooping, olive-green to brown when ripe, with darker markings between the seeds. Each pod contains 20–35 smooth dark green to brown cylindrical seeds 3–4 mm long.
This annual shrub germinates in successive flushes in spring, summer and autumn. Seedling flushes may exceed 50 m2. Plants grow rapidly in summer, either as scattered individuals or in small to large stands. Growth rates can exceed 4 cm a day in summer. The plant flowers from late spring to early autumn. A single plant can produce over 1,200 seed pods. When they dry out, seeds are scattered easily, and are quite long-lived in the soil. The plant in Butler Creek is growing near a serious infestation of Leucaena leucocephala. Although attempts are made from time to time to control the Leucaena, this is generally done after it has seeded and its vast number of long-lived seeds have dispersed. I can foresee an interesting battle between the two species.
Caterpillars of the Common Grass Yellow Eurema hecabe feed on the plant.
Photographs taken at Nelly Bay 2011
Page last updated 12th February 2017