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Chasing Madagascar Forest Grasses

Collecting Expedition: 5 October – 8 November 2011

Written by Maria S. Vorontsova, Royal Botanic Gardens Kew

Can grasses really live in forests? Yes. Forest shade grasses grow in damp areas and have wide leaves to help them capture more light. Millions of years ago forest grasses developed a new system of photosynthesis called C4 and became able to survive in hotter and drier open areas. Their modern descendants in the Forest Shade Clade are particularly diverse in Madagascar and reconstructing their evolutionary history will help us understand how the C4 photosynthesis system arose.

Poecilostachys ground cover in montane rainforest of Marojejy National Park. Many botanists walk through the rainforest looking upwards to search for flowering trees, but there are many interesting things to be found at ground level. (Photograph: Maria S. Vorontsova)

Reconstructing this evolutionary history is part of Russell Hall’s PhD research at the University of Sheffield. Russell planned this trip to collect fresh material for extraction of well preserved DNA. I came along to help identify the species and plan my future work on listing and describing all Madagascar grasses. We were lucky to work with local flora specialists including Franck Rakotonasolo, Mijoro Rakotoarinivo, Hélène Ralimanana, and Tianjanahary Randriamboavonjy from the Kew Madagascar Conservation Centre, Jackie Andriantiana from Parc de Tsimbazaza, and Guillaume Besnard from CNRS Toulouse.

Guillaume is placing specimens into orange desiccating silica gel to preserve the DNA while Maria is writing up collection notes. In the absence of a table in the wet forest the Kew landrover is very convenient!. (Photograph: Russell C. Hall)

Nobody has ever gone searching for forest shade grasses in Madagascar before, and we were anxious about not finding the right plants. We need not have worried: as soon as we entered the wet rainforest we could see nothing but a carpet of Poecilostachys, with broad leaves and long thin inflorescences. As we walked across elevation belts up the Marojejy mountain the shape of the inflorescences changed, and the length of the awns changed, and the leaves became more hairy. So now we have over 30 different collections of Poecilostachys, all similar but with myriads of subtle differences – identification is not easy!

Dense patch of flowering Oplismenus in a sunny spot in Marojejy National Park. The long thin awns stick to passing animals enabling dispersal. (Photograph: Maria S. Vorontsova)

Oplismenus is the only known grass genus with awns that produce a sticky secretion (awns are the long thread-like structures protruding from grass spikelets). How do the awns produce a secretion? And what is the dispersal mechanism? Nobody seems to know and nobody has ever researched this.

The next best thing after wet rainforest were the rice fields that have not been weeded. Damp areas at the bottoms of valleys and around streams have been converted into rice paddy fields throughout Madagascar, and as our car went around the bends in the road we had to keep our eyes peeled for untidy rice paddies with weeds. When the earth barriers separating the individual rice paddies are built or repaired Alloteropsis seeds in the soil germinate: the young Alloteropsis seedlings love water and are visually almost indistinguishable from rice plants. They go on to produce a dark tall panicles where the upper flower in each spikelet grows a long awn.

Plant collecting in the dark: Guillaume is using a torch to identify a species of forest Panicum while Russell is pressing Poecilostachys. (Photograph: Maria S. Vorontsova)

After five weeks in the field and 250 grass collections we feel confident that we have advanced the overall state of knowledge of grass diversity in Madagascar as well as finding material for DNA extraction to build a phylogeny of forest shade grasses.