This excellent info on medusoid euphorbias is from "Spiny Succulents: Euphorbias, Cacti, and Other Sculptural Succulents," by renowned nurseryman Jeff Moore, owner of Solana Succulents near San Diego. I highly recommend this new book for its excellent overviews, photos and readability. Jeff owns the copyright on the following excerpted photos and text, used here with his permission and my gratitude. -- Debra Lee Baldwin
Medusoid euphorbias, by Jeff Moore
"Nicknamed 'medusoid' for their Medusa-like halo of snaky tentacles that radiate out of a hypnotizing apex, these are some of the most prized of the euphorbias among enthusiasts. The most common form is Euphorbia flanaganii. The reason for its availability is that it will form new plants on stem tips, making propagation easy.
"Most, including such prized specimens as Euphorbia esculenta, must be grown from seed as they never form offsets. To complicate matters as always, but in a happy way, is that there are also myriad hybrids in cultivation, and some will offset, likely due to Euphorbia flanaganii parentage. Flowers are small but often quite abundant and long-lasting, mostly yellow but sometimes white or reddish. Prized specimens are often kept as container plants, but quite a few are suitable for in-ground planting.
Tricky Identification of medusoids
"There are a few that are easy spots, although even the ones I think I can identify on sight have a couple of visual allies, and then there are the hybrids. By far the most common medusoid as previously mentioned is Euphorbia flanaganii, as it is one of the few that freely offsets new plantlets, usually at the ends of its tentacle-like limbs.
"However, Euphorbia woodii and Euphorbia superans look very similar in my opinion. Euphorbia caput-medusae also stands out due to its longer arms and unique blooms. And you can spot a Euphorbia esculenta and be at least fifty percent sure you are right, as it could also be Euphorbia inermis. So as always, we do the best we can.
"Euphorbia esculenta and Euphorbia inermis are both outstanding ornamental plants, with thick, finger-like tentacles emanating symmetrically around a central core. I just wish I could tell them apart. Over time, these plants can form an almost two-foot radius, and in the true species will never form offsets. That is why some of these plants are rare, not because they are hard to grow (in fact both of these are very tolerant of extreme temperatures and indifferent watering schedules), but because you must grow new ones from seed.
"If I may indulge you with a look into my book-making process for a moment, the aim with this and all of my books is to be both inspirational and informative---a "coffee table" book that also works as a reference guide. I really want to get all the names right, or as right as I can get them---that is my job, both as a nurseryman and author.
"Having said that... I take a lot of photos of plants in private collections, nurseries, botanic gardens - wherever I see them (thank goodness we live in the digital age and I can afford to indulge in my hobby). However, most of the plants I'm shooting are unidentified. I'll ask an owner if they can confirm what I think it is, but I often get shrugs. Either the tag was lost, or it never had one, or quite often the owner just wasn't into the names. So I'm spit-balling with best guesses quite often.
Crested Euphorbia flanaganii
"Euphorbia flanaganii has a tremendous propensity to multiply. The specimen above is also exhibiting the beginnings of a crest.
Central crests of Euphorbia flanaganii have a tendency to contort into a smile or puckered grimace.
Medusoid Euphorbias: Pests and Problems
"Medusoid euphorbias are prone to harboring scale insects that hide under their tentacles, which can be controlled with a systemic pesticide.
"Powdery mildew is an occasional unwelcome visitor to euphorbias, particularly the medusoids. It seems to appear on plants in more shady and wet winter conditions.
"One home remedy is Tinactin antifungal spray. Really. Expert grower Peter Walkowiak recommends applying a horticultural oil via a spray bottle, followed by a systemic pesticide. With both remedies, repeating the process after a few weeks is a good idea, along with getting the plants into a sunny and dry location.
More cool photos
"In case you haven't noticed, I tend to bombard the reader with images, and I really shouldn't be just throwing out scattershot multiple images of the same plant or plants just for the heck of it, as I've done below. I'm not sure if these will add to your knowledge of the medusoids. But getting back to the inspirational part, ain't they cool?
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"Spiny Succulents: Euphorbias, Cacti, and Other Sculptural Succulents".
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Many cacti and succulents form geometric spirals similar to those of sunflowers, pine cones and nautilus shells. Spiral leaf arrangements funnel rain to roots, and keep upper leaves from shading lower ones. The arrangement of a plant’s leaves along the stem is phyllotaxis (from ancient Greek, phýllon “leaf” and táxis “arrangement”). Mathematically, spiral phyllotaxis follows a…