Hibiscus trionum, commonly calledflower-of-an-hour,[2]bladder hibiscus,bladder ketmia,[2]bladder weed,puarangi andvenice mallow,[2] is anannual plant native to the Old World tropics and subtropics. It has spread throughout southern Europe both as aweed and cultivated as agarden plant. It has been introduced to the United States as an ornamental where it has become naturalized as a weed of cropland and vacant land, particularly ondisturbed ground.
The plant grows to a height of 20–50 centimetres (8–20 in), sometimes exceeding 80 cm (30 in), and has white or yellow flowers with a purple centre. In the deeply pigmented centre of the flower, the surface features striations, which have been the subject of controversy about whether they act as adiffraction grating, creatingiridescence.
The pollinated but unripe seedpods look like oriental paper lanterns, less than 25 mm (1 in) across, pale green with purple highlights.
The flowers ofHibiscus trionum can set seed via bothoutcrossing andself-pollination. During the first few hours afteranthesis, thestyle and stigma are erect and receptive to receive pollen from other plants. In the absence of pollen donation, the style bends and makes contact with theanthers of the same flower, inducing self-pollination.[3] Although outcrossing plants seem to perform better than self-pollinating plants,[4] this form of reproductive assurance might have contributed to the success ofH. trionum plants in several environments.[5]
Initial studies showed that artificial replicas of the flower surface produced iridescence that bees could recognise.[6] Later work suggested that the irregularities of the plant cells and surface resulted in the periodicity of the striations being too irregular to create clear iridescence[7][8] and thus suggested that the iridescence is not visible to man and flower visiting insects.[9][10] More recent papers have presented evidence that the flower is both visibly and measurably iridescent,[11] and the striations have been shown to be sufficiently irregular to generate particularly strong scattering of light at short wavelengths, producing weak iridescence and a 'blue halo' (of which the halo is the dominant visible effect).[12] It has also been demonstrated that the blue scattering increases the foraging efficiency of bumblebees in laboratory environments,[12] although it remains unknown whether this effect translates to a meaningful advantage in the field.[10][11]
^Buttrose, M. S.; Grant, W. J. R.; Lott, J. N. A. (1977). "Reversible curvature of style branches of Hibiscus trionum L., a pollination mechanism".Australian Journal of Botany.25 (5): 567.doi:10.1071/BT9770567.
^Seed, L.; Vaughton, G.; Ramsey, M. (2006). "Delayed autonomous selfing and inbreeding depression in the Australian annual Hibiscus trionum var. Vesicarius (Malvaceae)".Australian Journal of Botany.54: 27.doi:10.1071/BT05017.
^Ramsey, M.; Seed, L.; Vaughton, G. (2003). "Delayed selfing and low levels of inbreeding depression in Hibiscus trionum (Malvaceae)".Australian Journal of Botany.51 (3): 275.doi:10.1071/BT02128.
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