Narrow-leaf bladder ketmia biology
Hibiscus verdcourtii  (was Hibiscus trionum var. trionum)
Family: Malvaceae (Hibiscus family).

Common names: Narrow-leaf bladder ketmia, Bladder ketmia, Flower-of-an-hour, , Rose mallow, Wild Goosberry.

Confused with: Wide-leaf bladder ketmia (Hibiscus tridactylites Lindley). The varieties can be distinguished by:

• Leaf shape - narrow leaf bladder ketmia leaves are 2 - 9 cm long and deeply divided with the lobes much wider at the middle and towards the tip than at the base, where wide leaf bladder ketmia leaves are 2-10 cm long and wide and the lobes are less uniformly wide at the tip.
• Flower colour - narrow-leaf bladder ketmia flowers have a deep purple throat, where wide leaf badder ketmia flowers are uniformly creamy white.

Description:

Seedling leaves - the seedling leaves are similar in shape with one leaf circular to broadly oval in shape and the other circular with a slightly flattened base, 7 – 16 mm long and 9 – 15 mm wide and on stems to 10 - 20 mm long.

Early leaves - the first true leaf is roughly circular with a number of rounded teeth. Successive leaves are three-lobed and deeply divided.

Adult leaves – are three-lobed, 20 - 90 mm long and 15 – 115 mm wide, borne on 20 – 65 mm long stems, with deeply toothed or indented leaf margins, often tinged with purple or red. There is some variability in leaf shape.

Mature plants – are erect, to 130 cm, with some branches semi-erect. Plants arise from a taproot to 100 cm deep. Adult plants have many branches that may be covered in sparse hairs. The stems are green-brown and sometimes purplish.

Flowers – the single hibiscus-like flowers are borne in the upper leaf forks, with five cream to yellow petals, with deep purple centres around 30 mm wide, on stalks 5 – 20 mm long.

Seed heads – the light-grey, papery, bladder-like seed heads are nearly see through at maturity, 10 – 20 mm diameter, are covered in soft hairs, have raised purple ribs (that are purple in colour prior to maturity), split into five segments on maturity and are easily broken off the plant when mature. There are 30 - 40 dull, light- to mid-grey or brown kidney-shaped seeds that are 2 mm and 1.5 mm wide that have a pimpled seed surface in each seed head.

Lifecycle/Biology: Narrow-leaf bladder ketmia seedlings emerge in successive seedling flushes. They can emerge at any time throughout the year after rainfall or irrigation. The densest flushes in excess of 200 seedlings/m2 are observed during the spring – autumn period. Soil disturbance increases seedling emergence. Rapid growth occurs, with flowering starting within 30 days. Flowering occurs throughout spring, summer and autumn, with large numbers of flowers observed a week or more after rainfall and irrigation. Flowers open for only part of a day, or at most one day and are self pollinated. Mature seed is also set rapidly, within 46 days. Seed production peaks in summer and early autumn but can continue year round on plants growing in sheltered conditions. Between 1,500 and 16,000 seeds can be produced on medium sized plants, and seed can be produced on plants that are less than 5 cm high. Narrow-leaf bladder ketmia is an annual plant. Plants are moderately frost sensitive, although some plants may persist in sheltered situations. The seed has strong dormancy after being shed with very little fresh seed germinating. Seed persists for a long period in the soil with 65% seed survival after two years.

Ecology: This plant is a common weed of summer crops, degraded pastures, disturbed areas, roadsides and wasteland. Cultivars of this variety are planted as garden ornamentals. It is found on a wide variety of soil types, and particularly on heavy cracking clays.

The problem: The plant is a common weed of irrigated and dryland cotton, sorghum, sunflowers, maize and other summer crops. This variety is more of a problem in eastern and cooler cotton growing areas. A large number of seeds are produced resulting in a persistent seed bank and problems in controlling this species over a number of years. The seeds persist for a long period in the soil. Seedlings emerge in successive flushes after rainfall and irrigation events. This makes control particularly difficult. Early control is important to prevent seed set, particularly by chipping and cultivation. While individual plants are not overly competitive, dense stands cause localised yield losses. Selective control using herbicides in cotton crops is difficult because cotton is similarly susceptible to a range of effective herbicides. Bladder ketmia is an alternative host to many insect and crop pathogens.

Distribution: Occurs throughout Australia

Origin:
Thought to be an introduced plant.

References:

Plants of Western New South Wales, p. 481.

Crop Weeds of Northern Australia, p. 134 - 135. The description is relevant for both wide- and narrow-leaf bladder ketmia. The central Queensland specimen pictured on page 135 is wide-leaf bladder ketmia (H. trionum var. vesicarius).

Johnson, S. B. Ecology and management of bladder ketmia (Hibiscus trionum) and other emerging problem Malvaceae weeds.

Compiled by
Graham Charles and Stephen Johnson