Thursday 18 February 2016

Increase in Mediterranean natives in British & Irish flora?

Giant Fennel: flowerhead above, leaf below
Images: C. Thorogood
Why, you may wonder, should British and Irish botanists be taking an interest in plants native to the Mediterranean Basin? Unless of course a holiday is in the offing! 

Because, as Bristol botanist Dr Chris Throrogood suggests below, we may start to see more Mediterranean natives turning up in the next few years, either as casuals or becoming established. 

In this guest blogpost, Chris also flags up a few distinctive aliens that botanists in southern parts of Britain and Ireland might like to watch out for this year:  
“The UK is predicted to develop a more Mediterranean climate with global warming in the 21st Century. With increasing temperatures and changing rainfall patterns we may see changes in our flora. In 2016 we’ve already seen more plants blooming out of season than ever before. 

We may also expect to see an increase in the abundance of aliens originating from the Mediterranean Basin as conditions in the UK become more similar to their native habitats. Two such examples are noteworthy from recent years and when they crop up you can hardly miss them!

Giant Fennel (Ferula communis) is a spectacular member of the Carrot family (Apiaceae) with tree-like stature. It is a common and prominent feature of Mediterranean roadsides in spring, with towering, woody inflorescences persisting long after blooming. Gardeners will know the plant takes years to build up a stock big enough to bloom. The species is casual in the UK and usually considered to be a garden escape. 

Bean Broomrape spike: above & below right;
close-up below left of individual flower
Images: C. Thorogood
There are some recently established quite spectacular stands of the plant along motorway embankments in Kent, which it shares with its more diminutive relative, the culinary Fennel (Foeniculum vulgare) – also a Mediterranean native. As our weather becomes warmer, we may see an increase in this impressive plant along our roadsides.

Bean Broomrape (Orobanche crenata) is rarely cited in UK plant field guides and is an uncommon, casual member of our flora. However when this parasitic plant does occur, it is often in spectacularly large numbers! I first saw this plant in the UK in Cranham, south Essex, where it has long been known since large numbers of it appeared as a pest on cultivated crops. It now re-appears sporadically there on field margins and fallow land on wild host plants such as Smooth Tare (Vicia tetrasperma). 

More recently, several million Bean Broomrapes infested Broad Bean fields in Kent. This extraordinarily large population presumably will have deposited a significant seed bank so the plant may well persist in the area for years to come. Worryingly for farmers, this outbreak suggests this common Mediterranean pest may well be on the increase in the UK.

Other ‘weedy’ broomrapes infect various crop species in the Mediterranean for which we should be on the lookout, particularly if farmers turn to new crops such as sunflowers. 

Branched Broomrape (close-up below)
Images: C. Throrgood
For example Branched Broomrape (Phelipanche ramosa; previously known as O. ramosa) which has long been recorded (though not recently) in the UK on various herbaceous hosts. 

With a recent resurgence in Mediterranean natives such as the two described above, and even remarkable observations such as the presence of desert species such as the Prickly Pear (Opuntia phaeacantha) naturalised in east Kent, it looks like we could see an increase in Mediterranean components of the UK flora in the future”.

Many thanks to Chris for alerting us to some of the Mediterranean natives we may start to see turning up more frequently in the south of these islands. And who better to record and map any such newcomers than BSBI botanists?

All of the species above (apart from the Prickly Pear) appear in Stace 3 (the “botanists’ Bible”!) but without illustrations, sadly. 

If you’d prefer to have colour photographs and line drawings to help you identify those aliens with confidence, or if you’re heading to the Med this year and fancy IDing them on their home turf, you might want to check out the sample pages here for Chris’s new field guide to the wild flowers of the western Mediterranean, which Kew Publishing are bringing out this month. 

The images and illustrations on this page are Chris's work - click on an image to enlarge it.

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