December, 2011: Euphorbia cyathophora, painted-leaf spurge, fire-on-the-mountain, wild poinsettia

Botany

December, 2011: Euphorbia cyathophora, painted-leaf spurge, fire-on-the-mountain, wild poinsettia

Euphorbia cyathophora (painted-leaf spurge)
Cyathia with brilliantly colored bracts.

Photograph courtesy of Rufino Osorio, © Rufino Osorio. All rights reserved.

Family: Euphorbiaceae, the Spurge Family

Distinguishing Characteristics: This is an erect, annual herb (short-lived perennial in tropical regions) that develops a taproot.  Stems are hollow and may be unbranched to many-branched.  Plants occasionally grow to 3 feet in height, but are more often in the 1-2 foot range.  When broken or bruised, the leaves and stems produce milky latex.  Leaf arrangement is alternate at the base of the plant and opposite or whorled along the upper portions of the stem.  Leaf shape is extremely variable, from long linear (like a blade of grass) to lance-shaped or fiddle-shaped.  Unlike the Christmas poinsettia, which requires short days/long nights to initiate flowers, the painted-leaf spurge may flower at any time of year.  The spurge family has a distinctive type of inflorescence, known as a cyathium, which consists of a single apetalous (lacking petals) female flower surrounded by several apetalous male flowers, all contained in a cup-like receptacle; these are often accompanied by brightly colored bracts (modified leaves) and nectar glands to attract pollinators.  The cyathium of painted-leaf spurge has a single gland (rarely two or three glands) and a whorl of bracts that are green with a red, pink or (rarely) white blotch at the base.  The bracts are as variable in shape as the leaves.  The fruit is a three-lobed capsule, approximately ⅙ inch wide, and contains three black to brown seeds that are uniformly tuberculate (covered with small warts).

Euphorbia cyathophora (painted-leaf spurge)
Plant with paler, linear cyathial bracts. Note the 3-lobed fruit characteristic of the Euphorbiaceae.

Photograph courtesy of Rob Bierman, Atlas of Florida Vascular Plants

Distribution: Painted-leaf spurge is native to the Americas, but its exact native range is obscure.  It is distributed through the eastern and central United States, the West Indies, Mexico, Central America and South America.  Most taxonomic references regard it as native to Florida.  It is occasionally cultivated, and it has become naturalized in the Old World.

Occurrence in Florida: This species is commonly found growing on disturbed sites, dunes and in hammocks throughout Florida.  It has been documented from 47 Florida counties.  It is often seen in open, exposed locations such as fallow fields, roadsides, abandoned lots and garden beds.

Similar Species in Florida: Painted-leaf spurge has long been confused with the fiddle-leaf spurge, Euphorbia heterophylla, another weedy species with a similar distribution.  In the past, some authors have treated E. cyathophora as a variety of E. heterophylla, but now botanists agree that they are two distinct species that can be separated by a suite of morphological characters:

Euphorbia cyathophora Euphorbia heterophylla
Flora bracts with red, pink or white blotch at base - uppermost bracts may be entirely red Floral bracts uniformly green, sometimes paler basally, but never with red blotch at base
Cyathial gland sessile (not stalked), with an elliptic opening, appearing bilabiate (two-lipped) Cyathial gland stalked, with circular opening
Seeds rounded, not keeled Seeds keeled, often trigonal (three-angled)
Seed surface finely and sharply tuberculate (warty) Seed surface coarsely and bluntly tuberculate

Means of Dispersal: In the Euphorbiaceae, the tissue of the fruit wall is elastic and contracts as the capsule opens, releasing the seeds balistically.  Such explosive dispersal moves the seed to a greater distance than if it were simply dropped.  Painted-leaf spurge occasionally escapes from cultivation.  Seed may also be dispersed in fill dirt and nursery stock.

Euphorbia cyathophora (painted-leaf spurge)
Close-up of cyathia, showing the unstalked glands with elliptic openings.

Photograph courtesy of Patti J. Anderson, DPI

Comments: This species has been the source of much nomenclatural confusion and has about a dozen synonyms (old names, no longer in use).  The Guide to the Vascular Plants of Florida (3rd edition) continues to refer to this species as Poinsettia cyathophora, but most other contemporary taxonomic references have transferred it to the genus Euphorbia.

Euphorbia prunifolia is listed as a noxious weed in Florida.  This name is now regarded as a synonym of Euphorbia heterophylla, the fiddle-leaf spurge.  Most taxonomic authorities regard this species as native to the southern United States, including Florida, so it may be advisable to remove it from the noxious weed list.

Euphorbia heterophylla (fiddle-leaf spurge)
Close-up of cyathia, showing the stalked glands with circular openings.

Photograph courtesy of Patti J. Anderson, DPI

Further Information: (no editor listed). 2011.  Euphorbia cyathophora Murray In: Euphorbia Planetary Biodiversity Inventory. Available from Tree of Life Knowledge and Information Network (TOLKIN): http://app.tolkin.org/projects/72/taxa/92925 (accessed 12 December 2011).

Oliveira, A.S. de and B. de Sá-Haiad.  1988.  Estudos taxonómicos sobre a família Euphorbiaceae Juss.-I: Euphorbia heterophylla L. e Euphorbia cyathophora Murr.  Sellowia 40: 5-31.

Turner, R. 1998.  Euphorbias: A Gardeners’ Guide.  Timber Press, Portland, Oregon.  192 p.

Marc S. Frank, Botanist
Florida Department of Agriculture and Consumer Services
Division of Plant Industry
1911 SW 34th St.
Gainesville, FL 32614