Plants: where to draw the line? (or, ICBN rules, OK!?)

Image: Carl von Linnés, Species plantarum (1753).

For years we can be happy using a word and thinking we know what it means, and presuming that everybody else also understands it in the same way. Well, what about the word ‘plants’? I realise I’m probably addressing many botanists here so we should at least be able to agree on what a plant is: but do we – and can we? Take, for instance, the name of this very column, ‘Plant Cuttings’; what is ‘plant’ in this context? Or the name of the journal in which this collection appears, the Annals of Botany (AoB). Botany is the study of ‘plants’ – but, again, what are plants in that context? Surely it’s obvious: plants are green things that photosynthesise. Well, maybe. But not all plants are green and they don’t all photosynthesise. And what about those – such as carnivorous plants – that photosynthesise but supplement their diets with animals? OK, can we agree that a plant is a member of the Kingdom Plantae then? Well, yes, but what about those large aquatic plant-like macro-algae that photosynthesise and are major primary producers in marine habitats? In a more pragmatic, inclusive approach I like to broaden the concept of plants to autotrophs more generally (but also include non-autotrophic members of Kingdom Plantae). But, if macro-algae are included, we can’t exclude autotrophic micro-algae; that would be ‘sizeist’. And since there is a long and noble tradition of including cyanobacteria (‘blue-green algae’, Kingdom definitely not Plantae) alongside the algae (because of their plant-like photosynthesis – amongst other features), we have a very broad definition of plants indeed. But broad is good, and useful. And if phytoplankton – ‘micro-algae (including cyanobacteria)’ – is good enough for our sister journal, the tautologically entitled AoB PLANTS (http://aobpla.oxfordjournals.org/), then who am I to be contrary. Well – and not wishing to make this long story overlong (although it is an important point I’m trying to make) – a pragmatic solution proposed by one of the Handling Editors of AoB was that a definition of plants could be organisms that are covered by the International Code of Botanical Nomenclature (ICBN – Cheers, Mike!). The ICBN is the rule book for botanical(!) names, binomials that are given to plants (great), fungi (which really aren’t plants, are they?) and ‘a few other groups of organisms’ [which includes cyanobacteria (yay!), chytrids, oomycetes, slime moulds, photosynthetic protists (micro- and macro-algae) and taxonomically related non-photosynthetic groups – hmm, where does it end?]. Well, that seems good enough as a working guide (and, pleasingly, means that all of the items – so far! – in ‘Cuttings’ are ‘legal’). Furthermore – and this is the real reason for delving into the semantic niceties of the term plants – this rather broad interpretation justifies me mentioning one of the most amusing plant stories of late, that of a new species of fungus named (and you really couldn’t make this up, though somebody clearly has!) Spongiforma squarepantsii. The fungus from the rainforests of Borneo – named ‘in honor of the famed cartoon character SpongeBob SquarePants, whose shape shares a strong resemblance to the new fungus. Moreover the hymenium when observed with scanning electron microscopy looks like a seafloor covered with tube sponges, reminiscent of the fictitious home of SpongeBob’ – was formally described by Dennis Desjardin et al. in Mycologia [2011; doi:10.3852/10-433]. Fun guys, these mycologists! (Mycologists that is who should really be botanists, per the ICBN…)

About Nigel Chaffey

Nigel is a botanist and full-time academic at Bath Spa University (Bath, near Bristol, UK). As News Editor for the Annals of Botany he contributes the monthly Plant Cuttings column to that august international botanical organ. His main goal is to inform (hopefully, in an amusing, educational, and entertaining way...) about plants and plant-people interactions.