Aquatic life
Water plant propagation methods
Water plants tend to propagate by means that are less available to most land plants. None of these methods are unique to water plants (except, possibly for turion formation) but they are mechanisms that water plants have refined greatly. Indeed, as far as propagation methods being unique to water plants is concerned, the more one looks into plant biology the less easy it becomes to actually define what is a water plant and what is a land plant - for there is no true distinction. I have seen water plants growing on land, often in relatively dry conditions! A list of such plants would include
- Callitriche - Starwort
- Nymphoides peltata - Fringed water lily
- Broad-leafed pond weed
- Veronica beccabungaBrooklime
- Cuckoo-flower
- Marsh pennywort
- Epilobium hirsutum - Great hairy willlow herb
Propagation methods
Most land plants can be propagated by means of cuttings, but in a water plant vegetative propagation by means of plant fragments has been taken to extremes as it can occur much more easily in water.As a result, many water plants take advantage of this method and have become very fragile to benefit by it. In these fragile plants the broken pieces very easily re-grow to form whole new plants, usually rooting at a leaf-stem node.
A list of such fragile plants would include such plants as
- Hydrocotyle ranunculoides - Floating pennywort
- Starwort
Some of the fragile plants are so viable that even a smallish piece of leaf will easily re-grow: these plants do not even require a leaf-stem node.
It appears that some water plants actually react to low light levels by root rotting or die-back. The plant, starved of light, cannot grow adequately so the roots rot, releasing the plant from the substrate. It then floats to the surface where roots grow again and it gets carried away, hopefully to come to rest somewhere new root growth can establish it once more.
This is not a mechanism I have seen mentioned elsewhere but is something I myself have observed in several plants, listed below. It would be a good subject for botanical research! It appears to me that smaller, younger plants, especially of species that propagate by stolons, release easier, which would make evolutionary sense as these small plants are the ones likely to be light starved by their older brothers.
- Water sprite
- Gymnocoronis spilanthoides - Senegal Tea
- Echinodorus tunicatus
- Epilobium hirsutum - Great hairy willlow herb
Turions are dense vegetative buds that some water plants form to over-winter. The turions remain when the plant dies in autumn and as they are denser than the water, they sink to the substrate when the parent plant rots. They remain on the bottom substrate until light levels (and possibly also water temperature) rise high enough for re-growth to start. The new growth is less dense than the turion so soon rises to the water surface to grow into a new plant. Clearly for plants to ue this method, water clarity needs to be good - or light levels will not rise high enough to cause spring growth, and water depth needs to be correct: too shallow anf the ice-bound turion may die, too deeo and re-growth will not happen. Water clarity is, of course, the mechanism that caused the Frog-bit to become nearly extinct in the Norfolk broads, where once it was common. High turbidity of the water (due to algae blooms caused by agricultural fertilizer run-off combined with mechanical disturbance from to many boats stirring up bottom silt) caused inadequate light penetration to the bottom so turions did not re-grow. It was therefore heartening to see (April 2005) young frog-bit in Cockshoot Broad.
Many marginal plants tend to grow too high for their stalks and roots - so they promptly fall over and re-root from the nodes. Plants that do this include
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Last modified: Fri, 24 Nov 2017 12:10:00 GMT
Page first published 21st January 2007
Page written and © by Richard Torrens
