A recent addition to the ‘Fossil Garden’ came in the form of Joinvillea ascendens Gauduch ex. Brongn & Gris (Syn. Joinvillea gaudichaudiana Brongn & Gris) from Hawaii ; a kind gift from the Royal Botanic Gardens Kew. It’s member of the Joinvilleaceae which in turn is a member of the ‘Graminid clade’ of the Poales – In short it is a sister to the world’s grasses.
Whilst the Poales certainly have their earliest roots in the late Cretaceous there is little fossil evidence to help us understand when and where they first evolved. The earliest recognisable fossils of this ethnobotanically important group come from 66 million years ago in what was South America. The Cyperaceae (The Sedges) have no fossil evidence from this period and their close relatives the Juncaceae (Rushes) have an even more limited fossil history. The earliest fossil evidence of this group belong to members of the Poaceae (the true grasses) and there is some fossil evidence that suggests that the Restionaceae was around at this time too. Another genus in the Poales known from Maastrichtian (Late Cretaceous) fossils is Typha (the true Bull Rushes) who’s fossil record is that of leaves, found in the Negev desert of Israel, called Typhacites negevensis. So what has all of this got to do with the Joinvilleaceae? Joinvillea is very closely related to grasses indeed and on first inspection you would believe it to be a grass. It is currently placed as sister group, with the Ecdeiocoleaceae, to the grasses. It’s flowers are pollinated by wind just like its kin yet it bears berries making it a real oddity in evolutionary terms. This feature is relictual for the Graminids and believed to be a earlier occurring feature than the dry seeds of the grasses. It also bares multi-cellular micro hairs like the grasses which alongside some other features proves that the three groups have a common ancestor.
Joinvillea’s obscure occurrence and unusual, relictual, features certainly demand it a small place among the ‘fossil’ plants in our little garden. I am certainly pleased to see this new piece in the puzzle of plant evolution take up its position as the only grass in our garden.