A plant which shows viviparous germination
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Answer:
Many of the mangrove plants show vivipary or germination of their seeds while still attached to the mother plant. All species of the family Rhizophoraceae, all species of Avicennia sp. and Aegiceras corniculatum exhibit this phenomenon.
Vivipary is simplest in Aegiceras sp. where the small banana-shaped seed germinates within the pericarp, its cotyledons forming a long tube enclosing the plume (Morton, 1990). Avicennia sp. shows further development with thick bright green cotyledons, folded double.
In species of Avicennia sp. and Aegiceras corniculatum, the embryo ruptures the testa and fills the pericarp which then starts to enlarge in proportion to the growth of the embryo. The species of Rhizophoraceae are well known for their long torpedo-shaped hypocotyls, hanging in cluster from the mature inflorescence. The hypocotyl pierces the fruit and grows out of it and this embryo seldom falls directly into the mud. Instead it floats horizontally and when anchorage is possible, bends itself up to vertical. In Bruguiera sp., the whole fruit falls from the plant with the hypocotyl still attached, and piercing its apex, so that the embryo grows cigar-like out of this base. The cotyledons are connate only at the base and their glandular epidermis takes nutrients from the pericarp to feed the hypocotyl. In Rhizophora mucronata, with a hypocotyl reaching sometimes up to 1 m in length, the hypocotyl falls out of the fruit base which is left attached to the plant. The two cotyledons are completely fused, with the plumule entrenched in them. They suck nutrients from the pericarp for the growth of the hypocotyl. The plumule often protrudes from the fruit and is demarcated by a grove from the hypocotyl.
The viable seedling can be water-borne over long distances and can take immediate advantage of opportunities at an advanced stage of development. It can be stated that the embryo development is more or less continuous and the dispersal takes place through seedlings, not seeds.
In Aegialitis, Acanthus, Avicennia, and Aegiceras species, the embryo does not rupture the pericarp. This condition is called cryptovivipary.
The main advantages of vivipary and cryptovivipary are as follows (King et al,. 1990):
1.
Rapid rooting
2.
Salt regulation
3.
Ionic balance
4.
Development of buoyancy
5.
Prolonged attainment of nutrients from the parents (= nutritional parasitism)
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