Annual or perennial herbs or shrubby plants, with simple or branched stems, which are topped by several-rayed umbel-like cymes. Leaves below the umbel usually scattered or alternate, without stipules, often broadened upward. Bracts of the umbel quite different from the stem-leaves; blades entire or toothed. Involucres sessile or peduncled, axillary, disposed in open or close cymes; lobes often toothed. Glands 4, transversely oblong, reni-form or crescent-shaped by the horn-like appendages, the missing one represented by a thin often ciliate lobe. Capsule exserted, smooth or tuberculate; lobes rounded, sharp or keeled. Seeds variously pitted, often with caruncles. [Greek, referring to the milky juice of these plants.]

About 250 species of wide geographic distribution. Besides the following, several others occur in western North America. Type species: Euphorbia dendroides L.

Leaves mainly opposite and decussate; capsules 5" wide or more.

1.

T. Lathyrus.

Leaves alternate or scattered; capsules less than 5" wide.

Leaves serrulate; glands of the involucre oblong, oval or orbicular.

Seeds smooth or faintly reticulated.

Glands stalked; warts on the capsules elongated; seeds faintly reticulated.

2.

T. obtusatus.

Glands sessile; warts on the capsules depressed; seeds smooth.

3.

T. platyphyllus.

Seeds strongly and prominently reticulated.

Glands nearly sessile; capsules warty.

Upper stem-leaves with small basal lobes; bracts of the umbel about as broad as long

or broader.

4.

T. missouricnsis.

Upper stem-leaves merely sessile; bracts of the umbel manifestly longer than broad.

5.

T. arkansanus.

Glands stalked; capsules smooth.

6.

T. Helioscopia.

Leaves entire; glands of the involucres crescent-shaped or reniform.

Plants perennial; seeds smooth.

Glands crescent-shaped, horned.

Stem-leaves 2"-6" broad; capsules smooth.

Leaves subtending, the umbel lanceolate or oblanceolate.

7.

T. Esula.

Leaves subtending, the umbel ovate, oval or obovate.

8.

T. lucidus.

Stem-leaves 1/4"-1 1/2" broad; capsules granular on the lobes.

9.

T. Cyparissias.

Glands reniform, not horned.

10.

T. Darlingtonii.

Plants annual or biennial; seeds pitted or rugose-pitted.

Leaves thin, petioled.

Capsules with 2-crested lobes.

11.

T. Peplus.

Capsules with rounded lobes.

12.

T. commutatus.

Leaves thick, sessile.

13.

T. robustus.