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Spotted Spurge

Euphorbia maculata

Description 2

Plants prostrate annuals, ascending in shade or competition; plants hairy; plants typically not more than 15 cm tall; usually forming mats less than 20 cm., individual stems generally less than 10 cm but may get to 20 cm or more. Largest internodes up to 2 mm in diameter. Stipules divided. Most leaves generally oblong and greatly unequal at the base; usually has a reddish-purplish “splotch” on the leaf but some individuals may have leaves that lack them; top of leaves usually glabrate to glabrous; shallowly serrated. Hair on fruits strigose. Seeds with shallow, rounded transverse ridges, often less whitened at the top of the ridges than other parts of the seed.

Comments 2

When reading descriptions like the one in Manual of the Vascular Plants of Texas (Correll and Johnston, 1979), it can be difficult to distinguish E. prostrata from E. maculata without looking at the seeds or hairs. The leaves are also quite different and can provide a good character to differentiate the two, especially in combination with the other characters:

Euphorbia prostrata: Appendages characteristically light purplish pink, as long as the gland is wide or shorter, all of equal or subequal width; glands magenta and smaller than those of E. maculata; cyathium peduncle as long or longer than the cyathium; oval to rotund leaves always lacking a "splotch"; leaf bases more equal than E. maculata (still unequal); hairs on fruits generally not appressed, if appressed, absent between the keels or at least sparser than the density on the keels; ridges on seeds coming to a sharp edge.
Euphorbia maculata: Appendages characteristically white (pink under stress), as long or longer than the gland is wide, those subtending proximal glands larger than those subtending distal glands; glands yellow to magenta and larger than those of E. prostrata; cyathium peduncle shorter than the cyathium; oblong leaves often with a reddish or purplish “splotch” on them (not always); leaf bases more unequal than E. prostrata; hairs on fruits always appressed and uniformly distributed; ridges on seeds rounded.

Because of the abundance of these two species as lawn and garden weeds, it is usually fairly easy to find the two species to compare.

During the 1930's and 1940's, Louis Cutter Wheeler (the Euphorbia expert of the time) called this species E. supina while giving the name E. maculata to a different species, now known as E. nutans, based on some misunderstanding of the type specimen. This has long since been resolved with the name E. maculata representing the smaller plant and E. nutans representing the larger plant (photos can be found here). Occasional specimens representing this outdated taxonomy can be found. For more information concerning this, please read The application of the Linnaean names of some New World species of Euphorbia subgenus Chamaesyce by Daniel Burch (1966, Rhodora 68:155–166; also available on JSTOR).

For information regarding spotted spurges without "spots", please read here.

Variation: Euphorbia maculata is quite variable. As such, I recommend viewing observations identified by me from your general area (state-level in the US or country-level elsewhere) before identifying. A link to the Texas observations I've identified can be found here (identify link). The variability manifests itself geographically, individually, phenotypically, and environmentally. In reality, the variability is likely not that much more extreme than many other species but is present due to its sheer abundance and frequency of being encountered by people. Geographic variability is greatest in the southeastern United States where it most likely evolved. In some ways, it is easier to recognize in the aformentioned region due to the lack of other confusing species except E. humistrata where the distinction between the two is technical and difficult regardless of where the two species occur. Individual variation is easily spotted in lawns and gardens overun with the species with the most striking example being observed in the spots. Phenotypically, earlier leaves are broader and more rounded than midstem leaves, which are broader and larger than bract-like leaves (more on this will be explained in a publication I am currently working on). Environmentally, the plant tends to have narrower leaves in drier conditions, is redder when stressed, produces broader leaves when trampled, and varies so widely under the various conditions that it may be exposed to that it cannot possibly be summarized here.

Relatives: The species is closely related to E. humistrata and E. meganaesos. Late-season plants are more difficult, but comparisons with E. humistrata can be made here. All three species can be distinguished by the following key.

(1) Plants glabrous ...............................................................................................................................................................E. meganaesos
(1) Plants hairy ..............................................................................................................................................................................................................2
(2) Plants rooting at nodes in later stages of growth; seeds smooth or somewhat granulate, not transversely ridged; [[field characteristics, very difficult to apply and partially under construction] early non-flowering leaves rounded apically; cyathial glands usually pink even when appendages are white, trending longer than those of E. maculata; fresh, non-damaged styles usually ca. 1/2 the length of the exerted ovaries or capsules, usually longer than the longest glands (often 2-3 times the length, especially when stressed, rarely less than 1.5 times the gland length) [field characteristics, very difficult to apply and partially under construction]] .......................................................................E. humistrata
(2) Plants not rooting at nodes, rarely rooting at internodes if buried in wet sand; seeds with rounded transverse ridges; [[field characteristics, very difficult to apply and partially under construction] early non-flowering leaves usually acute or subacute, rarely rounded; cyathial glands usually yellow when appendages are white except rarely in late-season plants, trending shorter than E. humistrata; fresh, non-damaged styles on exerted fruits ca. 1/3 the length of the exerted ovaries or capsules, shorter than or equalling the longest glands when fruits exerted from the cyathium (occasionally slightly exceeding the glands in populations of the southeastern US; not exceeding 1.5 times gland length) [field characteristics, very difficult to apply and partially under construction]] ...............................................................................................................................E. maculata

Sources and Credits

  1. (c) Nathan Taylor, some rights reserved (CC BY-NC-SA), uploaded by Nathan Taylor
  2. (c) Nathan Taylor, some rights reserved (CC BY-SA), http://www.inaturalist.org/guide_taxa/346778

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