Once a melastome flower has been pollinated, the next challenge is to get the seeds somewhere they can grow. The family has evolved two broad strategies for this, and they split it into major groups.
Strategy one: the capsule
Many melastomes, including Tibouchina and its relatives, Osbeckia and Dissotis, produce dry capsules. When ripe, the capsule opens, and a large number of tiny seeds fall out or are shaken out by wind and rain. The seeds are so small and light that they can be moved by wind, by splashing rain, in running water and by sticking to mud on animals, birds' feet and human boots.
This strategy suits open or disturbed habitats. A plant produces vast numbers of seeds, most of which will land in the wrong place, but a few will reach bare ground in good light.
Strategy two: the berry
Other lineages, notably the large tribe that includes Miconia, produce fleshy berries. These are often small, sweet and brightly coloured, ripening to purple, blue or black. Birds, bats and primates eat them and carry the seeds in their guts, depositing them away from the parent in droppings. This is called endozoochory.
Because the seeds are packaged with a food reward, the plant gets more reliable long-distance dispersal. In many tropical forests, melastome berries are an important food for fruit-eating birds, particularly during seasons when few other fruits are available. Larger-fruited genera such as Bellucia also feed mammals.
Seed banks
Many melastomes make so many small seeds that the soil underneath them accumulates a seed bank, a store of dormant seeds waiting for a trigger. The most common trigger is light. When a tree falls and opens a gap in the canopy, buried seeds receive more light and warmth and germinate. This is part of why melastomes are such prominent colonisers of clearings, landslides and burned ground.
The invasion connection
Traits that make a seed disperser successful at home can make it a problem abroad. A species with small, numerous, bird-dispersed seeds and a persistent seed bank has what it needs to spread quickly in a new place. This is exactly the profile of species such as Clidemia hirta, which is covered in the article on invasive melastomes.
Comparing the two
| Feature | Capsule | Berry |
|---|---|---|
| Fruit type | Dry, splits open | Fleshy, indehiscent |
| Dispersal agent | Wind, water, rain splash | Birds, bats, primates |
| Seed size | Very small | Small to medium |
| Typical habitat | Open or disturbed ground | Forest and forest edges |
| Examples | Tibouchina, Osbeckia | Miconia, Bellucia |
For growers
Knowing the fruit type helps with propagation. Capsule seeds are dust-fine and need to be sown on the surface of the growing medium (growing melastomes from seed). Berry seeds are best cleaned of pulp and sown fresh.
Takeaways
- Capsule-bearing melastomes rely on wind, water and chance.
- Berry-bearing melastomes rely on animals.
- Both strategies produce many small seeds, and both help melastomes colonise gaps.
- Those same traits explain why some species become invasive.