I never cease to be amazed that garden centres and nurseries actually sell seeds and plants of the Mexican fleabane, Erigeron karvinskianus. In my garden, nothing (except perhaps the dreaded pellitory) flourishes and reproduces better, and it grows best in no soil at all. (I am not one of those who like their paving clean and unencumbered by plants in the cracks.)
Common (non-Mexican) fleabane (Pulicaria dysenterica) is widespread over Europe and western Asia, and got its English name from its believed power to drive off fleas, though I can’t find out whether you use the flowers or leaves for this. The leaves have a soap-like smell, and the sap is astringent and can be used in the treatment of dysentery, as can the root. Don’t try this at home – and certainly don’t rub the flowers or leaves on to your pet, as the plant is toxic to cats and dogs.
There are (naturally) two complications with the naming: pennyroyal (Mentha pulegium), used as an insect repellent, is also sometimes called fleabane; moreover, John Gerard’s Herball (1597) also brings in Conyza or fleawort, and argues about the nomenclature of fleawort versus fleabane …
In English-speaking parts of the Americas, P. dysenterica is known as ‘false fleabane’, because they have their own fleabanes, in the Erigeron family. Also classed among the daisies (Asteraceae), there are over 200 species of Erigeron worldwide, of which E. karvinksianus is native to Mexico and central America, but has been introduced and effectively been naturalised in most parts of the world. (Sir Humphry Davy noted in 1813 that ‘Canadian’ fleabane had been found in Europe.) Its English names include Latin American fleabane, Santa Barbara daisy, Spanish daisy, Karwinsky’s fleabane, or bony-tip fleabane.
The genus was named by Linnaeus, but this species was first described in 1836 by Augustin Pyramus de Candolle (1778–1841), the Swiss botanist, in his famous Prodromus Systematis Naturalis Regni Vegetabilis (begun in 1824 and completed – by his son Alphonse Pyramus de Candolle (1806–93) – only in 1874). The word comes from the Greek ἦρι (‘early morning’) and γέρων (‘old man’), apparently because the fluffy seedheads appear very quickly after flowering.
The specific epithet honours Baron Wilhelm Friedrich Karwinski von Karwin (1780–1855), born in what is now Hungary, but a Bavarian. (The spelling of his name is various: Karwinski, Karvinski, Karwinsky, etc.) A geologist and botanist, he collected in Brazil between 1821 and 1823, and made two expeditions to Mexico (1827–32 and 1840–3), the latter on behalf of the Russian government, sending back altogether more than 4,000 herbarium specimens, as well as fossils, and live cacti and succulents. He found what was later named E. karvinksianus in Oaxaca, Mexico, during his 1827–32 journey. Sadly, I can’t find a picture of him.
As well as the Erigeron species, the genus Karwinskia (buckthorn-like trees and shrubs) was named for him by Joseph Gerhard Zuccarini (1797–1848), professor of botany at Munich (who also worked on the classification of Siebold’s Japanese collections, but who was a plant-hunter in his own right).
Probably the best-known Karwinskia in Europe is K. humboldtiana (eating which leads to paralysis and death, though not for a few days after consumption).
He was also the eponym of a cactus, Mammillaria karwinskiana (the name bestowed by Carl Friedrich Philipp von Martius), Eupatorium karwinskianum (of which he collected the holotype, now in the Munich herbarium), various other plants and grasses, and a rather nice butterfly, Smyrna karwinsiana.
In the tropical islands of the Indian and Pacific Oceans, Australia, New Zealand and South Africa (as well as Portugal), E. karvinskianus is considered an invasive plant or High Risk Weed, and may not be imported. It is very hardy in the UK, but apparently cannot cope with regular seriously cold winters. It reproduces (by seed) readily in almost all soils (it also has rhizomatous roots, and so also bulks up quite rapidly on the spot), and as noted above, it will grow vigorously in soil-less crevices. (It was apparently planted between the steps of the Azteca Stadium in Mexico City for the 1970 Olympic Games, which must have looked wonderful.)
As so often (in my opinion, anyway), the various varieties of E. karvinksianus which have been bred in the last two-hundred-odd years are not as attractive as the original species. There is ‘Blütenmeer’ (‘Abundance of Blossoms’), and ‘Profusion’, which I am guessing is the same thing. Or there is ‘Stallone’ (?!), which has an Award of Garden Merit, but looks from photographs rather more bulky and thuggish than the species.
You can often see it growing on the sides of stone steps and in the crevices of stone walls, where it looks amazingly romantic. Next year, I must try planting it as an edging in some of my larger pots, with something bigger in a toning colour rising up above it – this will involve a mental note to self to start cultivating it deliberately rather than by most happy accident, but there is plenty of time, as it will still be flowering and setting seed well into October.