Subtribe D i m e r i i n a e

The probable line of evolution within the spikelets of Pogonachne (subtribe Ischaeminae), Nanooravia and Dimeria (subtribe Dimeriinae): A. Spikelet of Pogonachne racemosa Bor; B. Spikelet of Nanooravia santapaui (MR Almeida) Kiran Raj & Sivad.; C. Spikelet of Dimeria gracilis (sect. Capillares); D. Spikelet of D. kurumthotticalana s.l. (sect. Loriformes)

 

The subtribe Dimeriinae is considered one of the little-known groups of the tribe Andropogoneae and is represented by two genera, viz, Dimeria R.Br. (~ 55 spp.) & Nanooravia KiranRaj & Sivad. (1 sp.). It occupies rather an anomalous position in the classification due to its unique morphological characteristics like the presence of continuous tough rachis, and laterally compressed pedicelled spikelets with no trace of pairing (KiranRaj, 2008). Recent molecular studies with less representative taxa suggest that Dimeriinae falls within the circumscription of another poorly studied subtribe, Ischaeminae,--represented by 5 genera, viz. Ischeamum (~ 75 spp.),  Andropetum (1 sp.), Kerriochloa (1 sp.), Pogonachne (1 sp.) and Triplopogon (1 sp.) (Welker et al, 2020). Both subtribes are together represented in Peninsular India with about 90 described species (out of 130 spp. in the World) and 5 genera. Among these, 51 species and 3 genera (Nanooravia, Pogonachne & Triplopogon) are exclusively found endemic to Peninsular India.

From the morphological point of view, the merging of the subtribe Dimeriinae (having solitary spikelets borne in 'robust' raceme rachis ) into the subtribe Ischaeminae (having paired spikelets borne in 'fragile' raceme rachis) is doubtful and remains unsatisfactory. A meaningful systematic study with more representative taxa is essential to arrive at a final conclusion of merging these subtribes.

D I M E R I I N A E Hack. in Engl. & Prantl, Nat. Pfl. –Fam. 2, 2: 22. 1887. 

– Type:  Dimeria R. Br. 

Annuals or perennials. Inflorescence terminal, of single or digitate racemes with tough or fragile rachis. Spikelets single, pedicelled, usually laterally compressed but sometimes rounded; glumes subcoriaceous to crustaceous, keeled or not, often winged, smooth or echinate towards apex, margin often winged; lower floret reduced to a barren lemma; upper lemma oblong, bilobed, with a slender or stout awn; stamens 2 in number.

Occurrence & Distribution: 2 genera (Dimeria R. Br. –56 spp., Nanooravia Kiran Raj & Sivad. – 1 sp.). Tropical Asia extends to Australia and Madagascar, mainly Peninsular India with 22 endemic taxa.

Ref:- Kiran Raj, M S. 2008. https://hdl.handle.net/10603/7030 || Welker et. al. 2020. https://doi.org/10.1111/jse.12691

Dimerias in Peninsular India

A 'Dimeria-field' (mature stage) in Northern Kerala

Dimerias dominates the herbaceous stratum of western peninsular regions of India during the period of retreat-monsoon (September–November). Members of Dimeriinae are particularly abundant in Western Peninsular India, which includes the Northern Western Ghats and its coastal zone and the Southern Western Ghats region.

The highest concentration of species is found in Southern Western Ghats. In fact 28 of the 42 Peninsular Indian taxa (including 7 varieties) can be found in this small region from the South of Goa, Karnataka, Kerala to Tamil Nadu states. 17 taxa are exclusively endemic to this region. The high degree of endemism in the Peninsular Indian region (especially in the Western Ghats), both within Dimeriinae and among its allies, suggests that the subtribe originated in this area. (excerpts from Ph. D. thesis).