by Richard Corlett

Ecology only makes sense in the light of evolution, so a correct understanding of phylogenetic relationships is a fundamental requirement for almost any ecological research. The rapidly increasing availability of DNA sequence data over the last 10-15 years, coupled with improved methods for analyzing these data, has transformed our views of the relationships between organisms. However, for much of the last decade, changes have been so rapid – and, in some cases, so controversial - that ecologists have been reluctant to adjust the classification systems with which they are familiar. For flowering plants, at least, this caution is no longer justified. Thanks, in part, to the collaborative approach adopted by plant phylogeneticists, the new phylogenetic understanding of the angiosperms at the family level and above has reached a level of comprehensiveness and stability that removes any excuse for ignoring it (as the two most recent checklists of the Hong Kong flora - Corlett et al. (2000) and AFCD (2002) – unfortunately did). When I have time (i.e. when pigs fly), I intend to produce a generic checklist of our flora that reflects the new phylogenetic classification. In the meantime, here are some highlights of the major changes as they affect the Hong Kong flora. I have followed the most recent publication of the Angiosperm Phylogeny Group (APG 2003), but it is easier to find current information on their regularly updated website (www.mobot.org/MOBOT/Research/APweb/), although it differs in some details.

The following major local families have not survived the revolution at all: Aceraceae (= Sapindaceae), Asclepiadaceae (= Apocynaceae), Capparaceae (= Brassicaceae), Chenopodiaceae (= Amaranthaceae), Flacourtiaceae (= Salicaceae), Sterculiaceae (= Malvaceae), and Tiliaceae (= Malvaceae). The Euphorbiaceae has survived, but most of the local woody genera, including Antidesma, Aporosa, Bischofia, Bridelia, Glochidion and Phyllanthus, are now in a separate family Phyllanthaceae. The Hamamelidaceae loses Altingia and Liquidambar to the Altingiaceae, the Caprifoliaceae loses Sambucus and Viburnum to the Adoxaceae, the Loganiaceae loses Buddleja to the Scrophulariaceae and Gelsemium to Gelsemiaceae, and the Theaceae loses Adinandra, Anneslea, Cleyera, Eurya and Ternstroemia to the Ternstroemiaceae. As for the Scrophulariaceae, I do not have the space to explain all the changes. Suffice it to say that Lindernia, Veronica and several other genera are now in the Plantaginaceae, along with Callitriche. Other noticeable changes among the dicots are the inclusion of Avicennia in the Acanthaceae and the separation of Maesa as the Maesaceae.

Fig.1. Aporusa dioica, now in the Phyllanthaceae

There are also a lot of changes among the monocots, but, since I did not really believe in the Anthericaceae, Convallariaceae, Phormiaceae et al. anyway, I will have less problem adjusting to these changes than those botanists brought up on Dahlgren’s narrowly defined families. Here, the APG (2003) authors – rather irritatingly - offer several alternative options, with their current recommendations putting the Anthericaceae in the Agavaceae, the Convallariaceae in the Ruscaceae, and the Phormiaceae (Dianella in Hong Kong) in the Hemerocallidaceae. I never liked the monocots much anyway!

I am oversimplifying things a lot. Some of these proposed changes come with a great deal of support. There is no reasonable argument for continuing to recognize families that have been shown to be polyphyletic (e.g. Flacourtiaceae or the old, world-dominating, Mega-Euphorbiaceae) or to be nested within another family (e.g. Asclepiadaceae). Other proposals are more tentative – some differ between the text, the appendix and the website! – and a few may still change again as more taxa and more molecules are sampled. It should also be remembered that evolution does not always produce well-circumscribed families, so decisions on whether or not to combine sister groups under one umbrella are often more or less arbitrary.

Fig.2. Asclepias curassavica, now in the Apocynaceae

Bibliography

AFCD. (2002). Check List of Hong Kong Plants 2001. AFCD & SCIB, Hong Kong.

APG. (2003). An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG II. Botanical Journal of the Linnean Society 141: 399-436.

Corlett, R.T., Xing, F, Ng, S.C., Chau, K.C. & L.M.Y. Wong. (2000). Hong Kong vascular plants: distribution and status. Memoirs of the Hong Kong Natural History Society 23: 1-157.

Fig. 3. Eurya chinensis, now in the Ternstroemiaceae.