Establishing a common classification with APG III

The Angiosperm Phylogeny Group (APG) is an international group of botanists that aims to establish a common view on the classification of flowering plants, based mainly upon evidence gained from analyses of plant DNA sequences. The first APG classification was published in a ground-breaking paper in 1998. Since then the classification has been refined through two further updates.

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05 Mar 2010

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Ornamental onions (Allium sp.) at Kew. The APG III classification includes onions in the family Amaryllidaceae (Amaryllis family) that also includes daffodils (Image: G. Kite).

Following our previous article on the publication of APG III in January this year, this item considers some of the issues relating to this classification and tells more about how scientists at Kew helped to address them. Kew recently adopted APG III as its classification for flowering plants.

Understanding flowering plant relationships with APG III

As a result of the new classification, higher-level relationships of the flowering plants are now much better understood and supported than in 1998, and the number of plants whose relationships were previously uncertain has been dramatically reduced.

The number of unplaced eudicots has dropped significantly (now down to just five genera/families). APG III recognises 14 new orders in the eudicots, these the result of much more clearly understood relationships relative to APG II (2003). Read more about APG III classification here.

Kew scientists address the issues

APG III was published in the October 2009 issue of the Botanical Journal of the Linnean Society. In addition to the classification paper, three accompanying papers addressed other issues surrounding APG III. The first was a paper by a team of authors led by Elspeth Haston (Royal Botanic Garden Edinburgh) and Mark Chase (Kew) that outlined a suitable linear order for arranging herbarium collections or order beds in botanical gardens.

The second was a proposal by Mark Chase (Kew), James Reveal (Cornell University) and Mike Fay (Kew) for a subfamilial classification for three enlarged families of Aspagaragales: Amaryllidaceae, Asparagaceae and Xanthorrhoeaceae.

In APG II (2003), there were alternative narrower circumscriptions proposed for these three families, but these ‘bracketed’ circumscriptions were not popular so in APG III they have been removed. However, the recognised heterogeneity of these families makes them unwieldy for specialists working on either the taxonomy or attributes of the narrower families, so to improve communication a formal set of subfamilies is proposed.

Angiosperms downgraded

The last paper, by Mark Chase and James Reveal, is a formal supraordinal classification of the land plants that includes the ordinal and familial structure of APG III and overlays a set of superorders for the angiosperms within a single subclass. The angiosperms have previously always been classified at a taxonomic level too high relative to the other green plants, and this classification rectifies this problem.

Discover APG III in Kew's Shirley Sherwood Gallery

Art of evolution shirley sherwood exhibition image

Painting from Kew's 'Art of Plant Evolution' exhibition

The Art of Plant Evolution exhibition in the Shirley Sherwood Gallery displays paintings arranged in the APG III classification, and illustrates how recent genetic discoveries have changed the nomenclature and evolutionary sequence of many plants during the last ten years.

The paintings included in the exhibition display a sampling of the plant world, including algae, mosses, ferns, conifers and flowering plants, as well as some fungi. The 136 paintings by 84 artists cover 50 orders of plants in 118 families for a total of 133 species, providing a sweeping overview of the evolution of plants on earth.

Date & Time - Open during Garden opening times until 11th April 2010

Location - Shirley Sherwood Gallery at Kew Gardens

Tickets - Free once inside the Gardens. Buy tickets online.

Kew Publishing - Exhibition catalogue The Art of Plant Evolution (by S. Sherwood & J. Kress, 2009, Kew Publishing) accompanies the exhibition.

Article first published in Kew Scientist

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