Fire Opens Seed Capsules

a burned tree with clam-shaped seedpods is seen against a blue sky background

Biological Strategy

Banksia

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Sense Temperature Cues From the Environment

Some living systems use their ability to perceive temperature to find prey or avoid predators, or as a way to gain information about their environment, such as whether they are near a warm or cold place. Temperature gradients can be subtle and modulate as they travel through water, air, or solids. Living organisms must therefore have a variety of thermal sensors appropriate to a given medium (liquid, gas, solid). Some even have a way to “visualize” a signal’s source. For example, the rattlesnake has heat sensors with thousands of nerve endings located in pit-shaped holes on each side of its face. The sensitivity of the pits overlaps, giving the snake a bifocal image of the heat’s source.

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Disperse Seeds

Plants disperse their seeds using a variety of mechanisms, including wind, rain, and attachment to animals. Seed dispersal can be important if plants growing too close together will compete for resources, such as nutrients and sunlight. Since plants are literally rooted in place, seed dispersal is also an important mechanism for expanding their range or reaching new environments.

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Flowering Plants

Clade Angiosperms (“receptacle seed”): Dandelions, oaks, grasses, cacti, apples

With 416 families containing some 300,000 known species, angiosperms are the most diverse group of plants, and they can be found around the globe in a wide variety of habitats. They are characterized by seeds that grow enclosed in ovaries, which are enclosed in flowers. The floral organs then develop into fruits of myriad kinds and dimensions, from simple seed casings on maples to elaborate fleshy growths like papayas. The oldest flower known from fossils, Montsechia vidalii, appeared during the Jurassic Period 130 million years ago. They are the primary food source for herbivorous animals, which in turn makes them the indirect food source for carnivores as well.

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Seeds of Banksia plants are dispersed via two-valved seed capsules that open in high fire temperatures.

“Banksias are spectacular evergreen bushes and trees related to the proteas of South Africa but, with the exception of one whose range extends into the Pacific, they are totally restricted to Australia. Of the 75 or so species that exist, 60 grow only in this south-western corner [of Australia]. Their strange inflorescences consist of several thousand small florets massed together in a single spike and arranged in vertical lines, that in some species have a gentle spiral twist…They take several months to develop and then open over several weeks. Birds such as lorikeets and marsupials like the honey possum come to drink nectar from them and in the course of doing so pollinate them. Usually, however, only a small proportion of the florets produce seed. In some species, those that are unsuccessful remain attached to the flower head, forming a grey rather bristly fur…It takes about a year for the seeds to mature. Like the bottlebrush, some banksias will not shed their seeds unless there is a fire. Indeed, it is almost impossible to remove them from the plant because they are held in hard woody two-valved capsules. But as the flames scorch the branches, the intense heat causes the capsules to open. Their front ends resemble pairs of brown lips on the side of the furry spike…By releasing their seeds only in the wake of a fire, the banksias ensure that they will fall on well-cleaned, brightly-lit ground recently fertilised with ash and so get the most favourable of starts in what is, even at best, an extremely harsh and demanding environment.” (Attenborough 1995:188-190)

Last Updated October 13, 2016

References

Book

The Private Life of Plants

BBC Books | 21/08/1995 | David Attenborough

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