Perhaps, like me, the poinsettiaful Christmas Show at Allan Gardens is still on your to-see list this year. Or perhaps you’re one of the poinsettia haters I’ve tried to convert before. Either way, if you love botany you might be impressed by the sheer diversity – and yet sameness – of the poinsettia’s big family, Euphorbia. 

Sameness because, despite the lack of family resemblance in many other ways, like all botanical families they’re united by the form of their flowers. I don’t mean the showy “petals” we admire (or disdain) in poinsettias. I mean the unique flower form at the centre called a cyathium, which botanist Wayne Armstrong describes here.

These are a few of the 2000+ cousins in the euphorbia or spurge family (Euphorbiaceae – don’t you love the mouthfuls that are botanical names?). All are in the genus Euphorbia. Many other cousins have different names. One member surprised me: castor bean (Ricinus), one of the bad guys in Breaking Bad.

Our covergirl shot of Euphorbia ‘Fireglow’ shows how that flower form works. In euphorbias, the large dangly bit is the female flower and ovary. The whole flower structure or inflorescence in many euphorbias is tiny, almost insignificant – though less so in some species than others. The “petals” that produce most of that smashing colour are leaf-like structures called bracts. ‘Fireglow’ is behaving like a poinsettia, making its intense colour only at flowering time, in this case late May.

My garden has had success with cushion spurge (Euphorbia polychroma), which self-seeds here and there, flowering in welcome unison with spring bulbs in April and May. The pressures of growing in dry shade have meant that it hasn’t become a self-seeding pest. But that same shade also meant that I was a flop at trying to grow the cultivar E. polychroma ‘Bonfire’ for its lovely reddish foliage. Not enough sun to produce lovely reddish foliage.

Below is a rock garden plant, donkeytail spurge (Euphorbia myrsinites), that hints of the succulent wing of the family. The foliage by itself is fascinating, and I like the way the flowers billow over the armour stone in this Beach rock garden.

‘Ascot Rainbow’ euphorbia (Euphorbia x martinii ‘Ascot Rainbow’) has understandably many admirers. The Toronto Botanical Garden has used it extremely well in containers. But I became an ardent admirer – at the Mr.-Darcy-loves-Lizzy level of ardency – on seeing it (below) at the Montreal Botanical Garden. I have no hope of ever growing it in dry shade, so my admiration is limited to OPGs (Other People’s Gardens). Hopefully, yours.

Euphorbias can be perennials, succulents (as you’ll soon see), trees – the native form of the Christmas poinsettia – shrubs, and annuals, too. The one below with the common name snow-on-the-mountain has been spotted in Toronto gardens.

Like all euphorbias it produces a nectar that attracted the pollinators in this picture. But be warned that all euphorbias make an irritating milky sap if cut. Take care if you live with animals or small fry, or if you’re weeding out extras! Use gloves, and never rub the sweat from your eyes after touching.

Succulent euphorbias can closely resemble cacti. Euphorbias make thorns, while cacti make spines, although the difference isn’t always a snap to tell apart. In fact, you might not know which the plant below is – until it makes these leafy appendages. It’s Euphorbia trigona var rubra and you can learn how well it works as a houseplant from my go-to houseplant expert Mr. Subjunctive whom I also credit for this link explaining the difference between the two genera.

Also from Allan Gardens is the crown-of-thorns (Euphorbia milii) above. Clicking the image to launch the slideshow lets you see how tiny the flower can be. On a visit to the Dominican Republic many years ago, Mr. TG and I saw crown-of-thorns used extensively as hedging, which I’m sure was effective.

Rather than asking us to walk a straight line this holiday-party season, the local constabulary at a RIDE stop should ask us to pronounce botanical names. Try this one: Euphorbia tithymaloides spp. smallii ‘Variegatus’. Not only is its binomial polysyllabic, it has a whole batch of common names. Devil’s backbone has to be my favourite, but according to Dave’s Garden it also answers to Japanese poinsettia, slipper spurge, and redbird cactus.

Then, of course, there’s poinsettia, which started us off. I have till Jan. 7, 2018 to get to Allan Gardens for my yearly dose of euphorbia euphoria. How about you?