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://​aob​pla​.oxford​journ​als​.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…)

Nigel Chaffey. ORCID 0000-0002-4231-9082

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 educational, and entertaining way...) about plants and plant-people interactions.

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