Tuesday, 6 May 2014

Itching to identify Australian hibiscus relative

It took me a while to realise the bushy tree in our local park was a Cow Itch Tree, Lagunaria patersonia. I know the species but I'm more used to being more tree-like, with a visible trunk. Anyway, that's my excuse (along with the fading light) and I'm sticking to it.

Then when I tried to identify it from the flowers I was thrown for a while because they looked like some kind of strange Hibiscus. And indeed they are. Lagunaria is in Malvaceae family, along with Hibiscus and various other 'mallows'.

Embarrassing on both counts perhaps, but I like to think I know where to look for, and how evaluate, the relevant knowledge, even if at first I may be botanically baffled. So let's move on. (And a warning, this is another of those posts with lots of taxonomy and the like.)

In between my past and present sightings off a Cow Itch Tree, the plant family Malvaceae hadn't stood still. No sooner did I pronounce "Ah, yes, of course, Malvacae", than I discovered (or rediscovered to give me the benefit of the doubt) that Malvaceae has been the topic of much academic debate in recent years.

The Angiosperm Phylogeny Group is a collective of scientists (of the kind we call systematists) I've mentioned before. Let's call them The Group. Together they extracted DNA, correlated this with other evidence such as the way plants look, and then restructured the tree of life for plants.

Parts of the tree are relatively stable and not greatly changed from before their first publication in 1998. Elsewhere we have insights into the relationships between different groups of plants either from the first evolutionary trees in 1998, version II in 2003, or III in 2009. In some cases the position and/or circumscription of the family has bounced around between iterations.

The Malvaceae family is one that remains unsettled, even post-2009. Part of the problem is that there is no objective way to decide how big a family should be. Once we know the relationships between plants and how they merge together into successively larger units, we then have to decide where to draw a line through the branch and give that unit a name. The units have to have a common ancestor and include all its descendants, but within that constraint they can be as big or small as you like.

Stability, pragmatism and utilitarianism are usually guiding principles (in 2005, Peter Weston and I published a paper skirting around this issue in Australian Systematic Botany). In 2003 The Group found that some of the families closely associated with Malvaceae were tangled up with it, and there was no clear lineage you could hive off and call Malvaceae without increasing its size. They admitted that some of the subgroups (like Tiliaceae - including the Lime Trees I posted about last week - and the Sterculiaceae) were difficult to distinguish anyway and the new expanded Malvaceae would 'come as something of a relief'.

In between versions II and III, Martin Cheek from Royal Botanic Gardens Kew published (in Kew Bulletin) two new family names in what is called the order Malvales. Cheek's system of ten familes - called a 'novel dismemberment of Malvaceae' by the Angiosperm Phylogeny Group in 2009 - has not been widely accepted. It's said the families are difficult to tell apart and The Group comment on their website that 'the "very good reasons" for doing this are wanting'. For scientists this is pretty straight talking.

The Malvaceae Info sites sums up the current status with a line about lack of agreement on the placement of Malvaceae and its close relatives within the flower plants or on its subdivision. However the separation of the current broad family into its four traditional constiuents (Malvaceae, Bomabacaeae, Sterculiaceae and Tiliaceae) is 'untenable'.

So...to know that the Cow Itch Tree is in the Malvaceae doesn't mean as much as it used to, although eventually I'm sure we'll find out what holds the family together and some subtle and useful divisions within it. In the old days you could say it nestled in with hibiscus and abutilon. Today you'll find boababs, kapok, lime trees and the durian in there with it.

To say it's closely related to Hibiscus is useful and even though the flowers are more like other genera in the narrowly, and traditionally, defined Malvaceae this is a  helpful hint for identification.

It used to be that to know it's Lagunaria is to know that it's Lagunaria patersonia. Prior to 2006 there was only one species (albeit sometimes with two varieties or subspecies), growing naturally in mostly-coastal Queensland (perhaps from northern tip of NSW) and on two islands off the east coast of Australia, Norfolk and Lord Howe. Nowadays the mainland populations are usually called, conveniently, Lagunaria queenslandica. I'm assuming my local tree is of fair dinkum island origin, and still Lagunaria patersonia (sometimes miswritten as Lagunaria patersonii).

Lagunaria's closest relative, according to Malvaceae Info, is Howittia, a genus still with only one species, but this time growing only on the Australian mainland, further south, and again mostly near the coast.

The common names give you plenty of information too. The Cow Itch Tree tells you that the fruit (unopened in the picture above) is packed with fibre-glass-like hairs which are unpleasant when shoved down the back of your shirt by a so-called school friend. Norfolk Island Hibiscus tells you at least one place where it grows naturally and that it's related to a Hibiscus (note to self). Queensland Pyramid Tree gives you some idea of its shape (again note to self, although Queensland Blob Tree would be more helpful) and a bit more of its natural distribution, albeit now for the separate mainland species.

As for names like White Oak, Sally Wood, Sugar Plum Tree and Primrose Tree...well, who knows.

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