Ecology of Dimerias

Dimerias in the juvenile stage

The Dimerias are primarily C₄ grasses, which exclusively prefer the natural tropical climate. Dimerias enjoy monsoon climate in general, and are localized along the Tropical wet region.

The sprouting, flowering and fruit-setting of annual species occur within a period of 4 months. In lateritic plains (Western Ghats), the Dimerias usually sprout during October and completely dry out by the end of February. The seeds that fall and are deposited in the crevices of laterite remain there for almost 10 months and on getting the post-monsoon rain the seeds germinate.

Dimerias show remarkable colour changes as they grow from the juvenile to the mature stage. In some areas the colour of the vegetation shows a gradual change from green to golden yellow, and from green to reddish brown in some other places. This is attributed to the formation of pigments called anthocyanins.

Phytogeography of Dimerias

'Sea of Dimeria' along the lowland region of Western Ghats

In Dimeriinae, about 90% of the known world species can be found in the following three areas, viz. Peninsular India, Sri Lanka and Southern China. Most of the species are having restricted distribution in one of these 3 regions.

The distribution pattern inferred from the literature and herbarium data indicates that subtribe Dimeriinae was naturally distributed in the southern erstwhile Gondwanaland region, an area composed of Madagascar, India, Sri Lanka, Australia and South East Asia, especially the Malesian region.

Three species are restricted to Madagascar, and all of them are endemic. This geographical isolation of Malagasy species from other species of Dimeria by approximately 2000 km, indicate an interesting direct phytogeographical link between Peninsular India and Madagascar. Some species are also found in volcanic soils of Mascarene Islands. This distribution supports the geological data which indicated that the archipelagic connections existed between the Indian plate, the Mascarene plateau, Madagascar and Africa until 75 million YBP!

Dimerias: Habit & Habitat

The tufted habit of Dimerias (Annuals)

Most of the Dimerias (80 %) are annuals, the majority of which are laterite-loving, where as perennials prefer rocky crevices along mixed forest margins, rarely in high altitude meadows, or wet sandy plains along water courses. Monsoon plays a major role in the establishment and diversity of Dimeriinae in general. The humid tropical wet climate favours the successful growth, maximum diversity and endemism in Peninsular India.

• Annuals: Solitary (or few); Many & Tufted; Branched & Matforming
• Perennials: Tufted & rooting at lower nodes; Stoloniferous & creeping