Euphorbia esula

Leafy Spurge


Douglas Provincial Park

The single female flower is emerging from the top of the involucre.  Note the three bifid styles.  No male flowers have emerged yet.

The basic floral unit is a structure known as a cyathium.  The cyathium is composed of a cup-like involucre plus several male flowers, and a single central female flower, that are enclosed by the involucre.  The top margin of the involucre is lobed and contains four, brown, crescent-shaped glands.  The horns on the glands are prominent to absent.  The female flower emerges first from the top of the involucre, followed by the male flowers.  Each cyathium is subtended by a pair of bracts known as cyathophylls.

The cyathia are arranged in dichasial cymes.  The peduncle terminates in a central cyathium, subtended by what I refer to as tier 1 cyathophylls.  Adjacent to the central cyathium are two lateral cyathia, each subtended by what I refer to as tier 2 cyathophylls.  The central cyathium matures first and then withers.  Meanwhile, the lateral cyathia are exserted on lengthening peduncle branches.  Given enough time, each lateral cyathia produces two adjacent cyathia in a similar manner as the original central one, and the structure repeats and multiplies itself.

Most of the cyathia occur within a pseudumbel that terminates the main stem.  The pseudumbel consists of a terminal, sessile cyathium that is subtended by a whorl of pedunculate cymes.  Each of the peduncles is subtended by an involucre leaf.  The involucre leaves form a whorl at the base of the pseudumbel.

The rest of the cyathia occur within cymes terminating peduncles arising as branches from the main stem.  These peduncles can also be somewhat whorled.

The flowers themselves are much reduced.  The male flower consists of a single stamen with a joint at the junction of the pedicel and filament.  The pedicellate female flower consists of a single ovary topped by three bifid styles.  Petals and sepals are absent from both types of flowers.


Esula: Answers to key questions in Budd's Flora (BF)  and Flora of Alberta (FOA) leading to this species. 
bulletperennial; NOT [annual]
bulleterect plants; NOT [prostrate mat-like plants]
bulletleaves NOT very crowded; NOT [leaves crowded on stem]
bulletleaves more than 3 mm wide; NOT [leaves less than 3 mm wide]
bulletleaves usually not over 1 cm wide; NOT [leaves usually 1-3 cm wide]
bulletleaves linear or lanceolate; NOT [leaves obovate]
bulletleaves pointed at end; NOT [leaves rounded or blunt at end]
bulletstem leaves entire; NOT [stem leaves finely serrulate]
bulletupper leaves NOT with a white margin; NOT [upper leaves with a conspicuous white margin]
bulletinflorescence in terminal umbels; NOT [inflorescence in leaf axils]
bulletinflorescence NOT very leafy



Euphorbiaceae: Answers to key questions in Budd's Flora leading to this family.
bulletherbs; NOT [shrubs or trees]
bulletland plants; NOT [water plants]
bulletplants NOT parasitic on trees, rooted in soil or water; NOT [plants parasitic on branches of trees]
bulletplants WITH milky sap
bulletflowers with only one floral ring, with sepals but not petals
bulletstamens or pistils in separate flowers on the same plant; NOT [stamens and pistils in each flower]
bulletfruit splitting open at maturity
bulletfruit 3-seeded