A specimen of Martian ‘Walking Grass’ grows in a refrigerated dish of nutrient gel.
Kew Gardens, London
Biopods are mobile plant-like organisms of varying degrees of complexity. They produce energy by photosynthesis1 and find water and the minerals they need for growth by "walking" on their long tendril-like roots, which are tipped with fine hooks and hairs. The mechanism resembles the curling and uncurling of Mimosa leaves, but is much more rapid. When a suitable source is found, rapidly-growing root-hairs burrow into the soil. Since this process requires a good deal of energy they move out of shadows – reduced photosynthesis in the coiled roots causes them to slacken, so that tension in another root moves the plant into the light. This has been misinterpreted as a directed flight mechanism, since the plants seem to move away from danger – in fact they are simply moving out of the shadow of the thing that endangers them. This is seen most easily in the simplest biopod, 'Walking Grass'; If the roots are suddenly in shadow the hooks disengage and the plant literally springs an inch or two in a random direction, repeating the process until at least one root is in sunlight.
1Their green photosynthetic pigment is not chlorophyll, but a chemical similar to the xanthophylls found in algae on Earth.
Later I've dropped the Mimosa analogy and changed this to say that "The contractile tissue is similar to the muscles of Terrestrial animals, though the chemical process is different."