Euphorbia L.

(incl. Chamaesyce Gray, Poinsettia J. Graham)

Literature: Durand (1899), Verdus (1964), Smith & Tutin (1968), El Hadidi & Fayed (1978), Turner (1983), Oudejans (1990), Oudejans (1992), Turner (1994), Jauzein (1995), Heubl & Wanner (1996), Carter & Cullen (1997), Benedí & al. (2000), Govaerts & al. (2000), Radcliffe-Smith (2001), Lambinon & al. (2004), van der Meijden (2005), Bruyns & al. (2006), Mabberley (2008), Verloove & Lambinon (2008), Hoste & al. (2009), Jäger & Werner (2005), Jäger & al. (2008),  Sell & Murrell (2009), Stace (2010), Zimmermann & al. (2010) & Lambinon & Verloove (2012). The following references exclusively deal with subgenus Chamaesyce: Huguet (1969), Mulligan (1978), Huguet (1978), Klotz (1984), Koutnik (1987), Benedí & Orell (1992), Verloove & Vandenberghe (1996), Hügin (1997, 1998, 1999), Kervyn & Lambinon (2000), Georges & al. (2003), Schröck & al. (2006), Röthlisberger (2007), Morche (2011), Pahlevani & Riina (2011), Bátori & al. (2012), Halford & Harris (2012), Yang & al. (2012), Often & al. (2013), Mugnai & al. (2021). There is a vast literature dealing with the subgenus Chamaesyce (chiefly local treatments). Numerous additional references are found in the publications cited above.

As currently understood (see Zimmermann & al. 2010) Euphorbia is an exceedingly variable and nearly cosmopolitan genus of about 2000 species. It is particularly well-represented in the warmer regions of the world. About ten species are usually accepted as native in Belgium as well (or at least archaeophytic) but residence status of some is more or less controversial (Lambinon & Verloove 2012): Euphorbia amygdaloides L. (subsp. amygdaloides), E. cyparissias L., E. dulcis L. subsp. incompta (Cesati) Nyman, E. esula L. (subsp. esula), E. exigua L., E. helioscopia L., E. paralias L., E. peplus L., E. platyphyllos L. and E. stricta L. Generic limits of Euphorbia have long been contested. Especially the recognition of Chamaesyce as a distinct genus was controversial. It was traditionally merely included as a subgenus in Euphorbia (see for instance Govaerts & al. 2000, Lambinon & al. 2004, Bruyns & al. 2006, Mabberley 2008). However, Koutnik (1987) recommended segregation from Euphorbia and subsequently this viewpoint was increasingly followed (see also Radcliffe-Smith 2001). However, recent molecular phylogenetic research, on the contrary, strongly suggests amalgamation of all species with cyathial glands in a broadly circumscribed genus Euphorbia (Zimmermann & al. 2010). Yang & al. (2012) stressed that seven previous molecular studies, with ca. 1/3 of all species of Euphorbia sampled, always yielded the same results. In a broad sense Euphorbia is monophyletic and includes four subgenera. Subgenus Euphorbia accommodates all native species while subgenus Chamaesyce includes several non-native species in Belgium. These are represented in two of the 15 sections of this subgenus: section Anisophyllum, subsection Hypericifoliae that encompasses all prostrate spurges and section Poinsettia, subsection Stormieae with E. dentata s.l. and E. heterophylla. The present treatment of Euphorbia is in accordance with these concepts.

Euphorbia is economically important: it includes numerous ornamental and weedy species.

1       Leaves opposite, often markedly asymmetrical at base. Stipules present. Plant often procumbent, rarely erect. Always annual (Chamaesyce) === 2

         Leaves alternate or rarely opposite, symmetrical at base. Stipules absent. Plant usually erect (more rarely more or less procumbent). Perennial, biennial or annual === 11

2       Capsules and stem hairy === 3

         Capsules glabrous. Stem glabrous or hairy === 5

3       Capsules with all hairs appressed, uniformly distributed. Leaves usually with a central purplish spot === Euphorbia maculata

         Capsules with all hairs patent, hairy on angles only or hairy all over. Leaves not spotted === 4

4       Capsule mostly hairy on angles. Seed deeply transversely furrowed === E. prostrata

         Capsule hairy all over. Seed tuberculate-rugose, not furrowed === E. chamaesyce p.p.

5       Stem erect. Cyathia in clusters. Largest leaves > 15 mm long === 6

         Stem procumbent. Cyathia solitary in leaf-axils. Leaves mostly < 15 mm long === 7

6       Plant hairy (at least in upper part and young leaves). Capsule > 1,9 mm long === E. nutans

         Plant glabrous. Capsule < 1,9 mm long === E. glomerifera

7       Leaves 2-4x as long as wide, nearly entire, more or less falcate. Seeds with 4-7 very prominent ridges === E. glyptosperma

         Leaves variable, entire or serrate, never falcate. Seeds smooth or irregularly rugose === 8

8       Seeds (almost) smooth === 9

         Seeds irregularly rugose === E. chamaesyce p.p.

9       Leaves suborbicular, entire, retuse at apex. Plant rooting at nodes === E. serpens

         Leaves oblong, serrate, rounded at apex. Plant not rooting at nodes === 10

10     Stems densely hairy (longest hairs ca. 1 mm long). Seeds blackish or dark grey at maturity === E. vermiculata

         Stems glabrous. Seeds never dark at maturity === E. humifusa

11     Cyathial glands usually 1. Pubescent, weedy annuals. Leaves ovate-obovate (Poinsettia) === 12

         Cyathial glands usually 4, rarely more or only 2-3. Glabrous or pubescent annuals or perennials, weedy or not. Leaves most often lanceolate to narrowly elliptic (Euphorbia s.str.) === 13

12     Most leaves alternate, often very different in shape on a single plant. Leaf margin mostly finely serrate to subentire === E. heterophylla

         At least lowermost leaves opposite, all alike. Leaf margin mostly coarsely serrate === E. dentata s.l.

13     Leaves opposite, markedly decussate === E. lathyris

         Leaves alternate, never decussate === 14

14     Ray-leaves (bracts) fused at base === 15

         Ray-leaves not fused at base === 17

15     Capsule pubescent. Rays usually 10-20 === E. characias

         Capsule glabrous. Rays usually 5-10 === 16

16     Strongly rhizomatous. Young leaves leathery and shiny, (sub-) glabrous  === E. amygdaloides subsp. robbiae

         Not or shortly rhizomatous. Young leaves herbaceous and dull, pubescent below (native) === E. amygdaloides subsp. amygdaloides

17     Plant very glaucous. Leaves succulent and fleshy. Perennial, becoming woody at base === 18

         Plant not or hardly glaucous. Leaves succulent nor fleshy === 19

18     Rays usually 5-12. Plant procumbent. Cyathial glands with short, more or less dilated horns at apex. Capsule ca. 5-7 mm across === E. myrsinites

         Rays usually 3-6. Plant erect. Cyathial glands emarginate. Capsule ca. 3-5 mm across (native) === E. paralias

19     Cyathial glands orbicular to ovate, not horned === 20

         Cyathial glands horned === 25

20     Annuals (native) === E. helioscopia, E. platyphyllos and E. stricta

         Perennials === 21

21     Plant quite glabrous, very robust, up to 150 cm tall. Rays more than 5 === E. palustris

         Plant densely to sparsely hairy, much more slender. Rays 4-5 === 22

22     Cyathial glands 2-3 (except sometimes in terminal flowers). Tubercles on the capsule hemispherical === E. oblongata

         Cyathial glands 4. Tubercles on the capsule often twice as long as wide === 23

23     Long-rhizomatous. Stem scaly at base. Cyathial glands turning purplish after anthesis (native) === E. dulcis

         Not rhizomatous (plant emerging from stout stock). Stem not scaly at base. Cyathial glands not turning purplish after anthesis === 24

24     Ray-leaves ovate-obovate. Stem slender === E. brittingeri

         Ray-leaves orbicular. Stem stout === E. epithymoides

25     Annuals (native) === E. exigua and E. peplus

         Perennials === 26

26     Stem leaves 2-3 mm wide, linear (leaves on sterile shoots very crowded and still narrower). Plant 10-30(-50) cm tall (native) === E. cyparissias

         Most leaves 3-12 mm wide (leaves on sterile shoots never linear). Plant 30-90 cm tall === E. esula

Additional aliens: Euphorbia peplis L. (syn.: Chamaesyce peplis (L.) Prokh.) (SW-Eur., vector unknown) and E. seguieriana Neck. (syn.: E. gerardiana Jacq.) (Euras., ore?). The latter species was firmly established for several decades along river Maas near Maaseik in the second half of the 19th century. However, according to Durand (1899) the plants grew only on the Dutch side of the river. Euphorbia segetalis L. was recently recorded as a weed in containers with olive trees imported from the Mediterranean area (Hoste & al. 2009). Euphorbia falcata L. has been claimed as an alien (Lambinon & al. 2004) but no voucher specimens have confirmed this claim (Verloove & Lambinon 2008). Potential records proved to be erroneous and referable to native Euphorbia exigua.


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Mugnai M., Lazzaro L., Di Nuzzo L., Foggi B., Viciani D. & Ferretti G. (2021) Synopsis of Euphorbia section Anisophyllum (Euphorbiaceae) in Italy, with an insight on variation of distribution over time in Tuscany. Phytotaxa 485: 1-65.

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Taxonomic name: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith