Friday, June 21, 2013

Botany picture #77: Pimelea linifolia

Pimelea linifolia (Thymelaeaceae), New South Wales, 2011.

Systematists and taxonomists have their favorite groups, and it is usually hard to say why they like this one better than another. I, for example, am particularly fond of the asterids, the large subclade of the eudicots that has evolved fused petals (the other large subclade, the rosids, has free petals). This group includes plant families such as the Lamiaceae and Acanthaceae, on which I have conducted research before I came to Australia, and the Asteraceae, which I am studying now.

In general I am not overly fond of most rosids or monocots. There are, however, non-asterid groups that I also like very much, and the Thymelaeaceae are one of them although they belong to the rosids. I have no clear explanation but it is interesting to note that they have gone out of their way to pretend that they have fused petals like the asterids - the picture above sure gives the impression that we are dealing with a long, narrow corolla tube and four corolla lobes. But what really happened in the evolution of the family is something different: the tube is a hypanthium, a floral cup that merely pretends to be a corolla tube. What looks like petals are the sepals, and the real petals are lost (although in other members of the family they can still be seen as small scales at the flower orifice).

Pimelea is by far the largest genus of the Thymelaeaceae in Australia. The species are generally small to medium sized shrubs and have only two stamens per flower. The genus is easily recognized but it is harder to determine the species.

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