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Euphorbia botany lesson

June 30, 2010

This is my attempt to explain why I love Euphorbias...not just because of their incredible diversity, their amazing growth forms, and (admittedly sometimes subtle) beauty, but also because I find them fascinating from a botanical point of view.

Probably old news to some, but if it's not, read on if you'd like! And there will be some pics, eventually :)

Even so, this post will be a little dry :)

The genus Euphorbia, with some 2000 species, is one of the largest plant genera. It encompasses everything from well-known species like Poinsettia and Crown of Thorns to little-known obscurities, and giant (30M) trees to little gems that never grow larger than a few inches.

This genus was first described by Linnaeus in 1753. Most other plant genera have been relentlessly re-described over the years, split and combined, and plants moved from one genus to another.

But Euphorbia still stands, more or less as originally described. Why? Because of cyathia.

A "cyathium" (plural "cyathia") is a flower structure that's unique to Euphorbias. No other plants have this.

The main part of a cyathium is the "involucre" or cup. So-called because it really is shaped like a cup. On the edges of the cup grow the "nectar glands." Yes, they produce nectar to attract pollinators!

What's more interesting is what grows from the inside of the involucre. Flowers!

But these aren't typical flowers with petals and everything you'd expect flowers to have. Instead, they're flowers that are reduced to their essences....the reduced female flowers in Euphorbias retain only what makes them female, namely, the pistil. And the male flowers, likewise, only have their male parts, namely, the stamens.

If you look at the bottom of this pic, you can see how the male and female flowers grow out of the involucre: {{gwi:559644}}

But Euphorbias have a few tricks up their sleeve. Sometimes cyathia only produce female or male flowers. Sometimes they produce both. Sometimes a single plant will produce both, but only on separate cyathia. Sometimes a plant will produce cyathia with only male or female flowers.

Time for a few pics!

E. godana. The nectar glands, growing from the involucre, are bright orange in this species. You can see a few female flowers (their stigmas always divided into three in Euphorbia) and many male flowers.


E. tortilis with lots of male flowers, sinking into the sap from the nectar glands:


E. tortilis again, showing female flowers:


Usually the nectar glands just produce a lot of nectar:


Sometimes they get a bit crazy, like in E. albipollinifera:


As you can see from the diagram above, "cyathophylls" grow from the bottom of the involucre. Sometimes they're pretty:


...and sometimes outstanding:


Thanks to Riki for permission to use the above diagram, and you can find out much better info here!



Comments (16)

  • johnh_or

    Nice write-up and fantastic pics! I love this plant....
    You might enjoy this site....Frank is the Euphorbia GOD!!!!

    Here is a link that might be useful: EVERYTHING Euphorbia

  • beachplant

    Thanks for the lesson & pics. Euphorbias Rock!
    Tally HO!

  • plant_junkie

    Wow that was really informative. Thank you for that post! I really enjoyed it. I have yet to become a fan of the Euphorbias because of their toxic sap. Not a big fan of allergic reactions :)


  • lzrddr

    The sap thing is way overstated, at least from my experience. I have over 200 Euphorbias and only when I go out of my way to hack off branches does the sap issue become an issue at all. To me it is sticky only... unless I get it in my eye. Never had much more of a reaction than that (save Euphorbia tirucalli which seems to be a tad more irritating)... never heard too many people make the same complaints about the sap in Plumeria circles, and is basically the exact same stuff... I did a lot more pruning when I had plumeria so the sap issue was a lot bigger deal for me then than now, now that I have pretty much killed off all my Plumeria. Lots of other plants have nasty saps (Jatrophas, Synadeniums, Oleandar, even some Aloes and cacti)- some irritating, as well as incredibly staining saps. My main issue with the saps is they gum up my pruners. But my blue cedar does that even more so.

  • land3499

    Thanks all for the kind words!

    johnh_or, Frank Vincentz's site is a great reference. But it hasn't been updated since 2006, nor does he post any more...I hope he's okay!

    I'm with lzrddr, have never had an adverse reaction to Euphorbia sap, although I've never gotten it in my eye...that sounds painful!


  • norma_2006

    That was a terrific lesson, Are you near So. Calif. travel time of no more then 40 minutes? If so do you give programs? My group is looking for speakers, of course you will be paid. Norma

  • wandering_willow

    I know this is an old post, but I just wanted to compliment and thank you! I love euphorbias, and was very curious about what united this expansive genus - you really explained it better than any other site or book I could find!

    Thank you!

  • land3499

    Thx WW, your kind words are very much appreciated.

    GO Euphorbias! :)


  • hanzrobo

    Awesome! Very informative! I have only a few of these. I have avoided euphorbias partly because of the sap, mostly because they're not as easy to cultivate as other succulents. Any tips on propagation would be appreciated. I will check out those sites listed above.

  • blueskies12

    Excellent lesson!!! I am not all that interested in Euphorbias, but always love to learn, this was very informative. Reminds me that the last botany class I took did not even cover Cactaceae. :(
    Thanks, Jenna

  • amccour

    "I have avoided euphorbias partly because of the sap, mostly because they're not as easy to cultivate as other succulents."

    I've actually found Euphorbias to be a loooooot easier than cacti. This might sound weird but I feel like they give you better feedback when they're not happy, whereas cacti have a weird tendency to look fine up until they collapse.

    Also having looked at this again I think the E. Nyassae I have is either a Godana or has some Godana DNA in it. Because while it looks more or less LIKE anE. Nyassae, it has the growing habit and flowers of a Godana. Except they're coming out of where they would as per a Nyassae.

    I need to get pictures uploaded. That greenhouse had a lot of weird plants that I've never been able to properly identify.

    "never heard too many people make the same complaints about the sap in Plumeria circles, and is basically the exact same stuff..."

    Aren't Plumerias supposed to have worse sap, being closely related to Oleanders?

  • norma_2006

    First I want to thank you on the lesson you posted information that I didn't know, I didn't know that both the male and female parts can be on the same plant. I have to give some of my Plumeria plants away because I have allery problens. I kept only a few of this species. I find them easy to pollinate by hand. I have problems of gathering the seed. Norma

  • land3499

    >I've actually found Euphorbias to be a loooooot easier than cacti.

    For me, some (globulars/medusoids) are easy, but others (mostly the shrubby ones) are hard. The problem I have with the shrubby species is keeping them over the winter. I grow increasingly convinced that they need a lot of water, at least once every two weeks.

    amccour, not sure about E. nyassae vs. E. godana. The editors of the Euphorbia Journal say that they've never seen E. nyassae in cultivation. In any case, it should be easy to tell apart from E. godana:


    This is E. nyassae in habitat (from The Euphorbia Journal):


    Norma, thanks for your kind comment.

    Another way of looking at the Euphorbias is that they're either monoecious (from the Greek "one house"...meaning a single plant will produce cyathia with both male and female flowers) or dioecious ("two houses"...a single plant will produce either male or female flowers).

    One more factoid :) The shrubby species are all monoecious, and don't hybridize. The globular species (for example, E. obesa) are all dioecious, and are tramps, hybridizing with anything they can find. :)


  • amccour


    It's this thing.

  • amccour

    Which in retrospect doesn't really look much like a Nyassae OR a Godana.

  • land3499

    Agreed, it doesn't look like either.

    To me, it looks like one from the E. schinzii complex, maybe E. uhligiana (although it doesn't seem to have a caudex) or something close to that.

    Nice spine shields!


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