Wild Flowers of Pittsburgh

Euphorbiaceae

Three-Seeded Mercury (Acalypha virginica)

In the fall this unassuming little weed can take on some surprisingly beautiful and varied autumn colors in the bronze range. This little patch grew out of a crack in a concrete driveway in Beechview, where it was beginning to show off its autumn colors (and its triple seeds) in late September. It grows everywhere in the city, although normally we don’t notice it much.

Gray describes the genus and the species:

ACALYPHA L. THREE-SEEDED MERCURY. Flowers monoecious; the sterile very small, clustered in spikes; the few or solitary fertile flowers at the base of the same spikes, or sometimes in separate ones. Calyx of the sterile flowers 4-parted and valvate in bud; of the fertile, 3-5-parted. Corolla none. Stamens 8-16; filament short, monadelphous at base; anther-cells separate, long, often worm-shaped, hanging from the apex of the filament. Styles 3, the upper face or stigmas cut-fringed (usually red). Capsule separating into 3 globular 2-valved carpels, rarely of only one carpel. — Herbs (ours annuals), or in the tropics often shrubs, resembling Nettles or Amaranths; the leaves alternate, petioled, with stipules. Clusters of sterile flowers with a minute bract; the fertile surrounded by a large and leaf-like cut-lobed persistent bract. (Akalyphe, an ancient name of the Nettle.)

Fruit smooth or merely pubescent; seeds nearly smooth.

A. virginica L. Smoothish or hairy, 3-6 dm. high, often turning purple; leaves ovate or oblong-ovate, obtusely and sparsely serrate, long-petioled; sterile spike rather few-flowered, mostly shorter than the large leaf-like palmately 5-9-cleft fruiting bracts: fertile flowers 1-3 in each axil. — Fields and open places, N. S. to Ont. and Minn., s. to the Gulf. July-Sept.


Flowering Spurge (Euphorbia corollata)

A relative of the Christmas Poinsettia and Snow-on-the-Mountain, this plant easily fools us into thinking it has regular five-petaled flowers like a pink or a buttercup. Structurally, however, the apparent petals are actually bracts that surround a cluster of tiny flowers. Doubtless there is a moral lesson to be learned here, but we have not learned it yet. These plants grew in a sunny meadow in Sewickley Heights, where they were blooming in late August.

Flowers. Numerous; tiny and insignificant, but surrounded by five showy white regular bracts that look like petals; in irregular flattish umbels.

Leaves. Oblong-linear; blunt; entire; smooth; lower leaves more elliptical; alternate, but whorled at the base of the umbel of flowers.

Stem. Smooth; purplish; unbranched up to the whorl of leaves at the base of the umbel; about 3 feet (1 m) high.

The genus Euphorbia is enormous, so Gray helpfully divides it into sections. Here he describes the genus, the section, and the species:

EUPHÓRBIA L. SPURGE. Flowers monoecious, included in a cup-shaped 4-6-lobed involucre (flower of older authors) resembling a calyx or corolla, and usually bearing large thick glands (with or without petal-like margins) at its sinuses. Sterile flowers numerous and lining the base of the involucre, each from the axil of a little bract, and consisting merely ol a single stamen Jointed on a pedicel like the filament; anther-cells globular, separate. Fertile flower solitary in the middle of the involucre, soon protruded on a long pedicel, consisting of a 3-lobed and 3-celled ovary with no calyx (or a mere vestige). Styles 3, each 2-cleft; the stigmas therefore 6. Pod separating into three 1-seeded carpels, which split, plastically into 2 valves. Seed often caruncled (ours only in §§ 5 and 6). — Plants (ours essentially herbaceous) with a milky acrid juice. Peduncles terminal, often umbellate-clustered; in the first section mostly appearing lateral, but not really axillary. (Named for Euphorbus, physician to King Juba.)

§ 4. TITHYMALÓPSIS (Klotzsch &. Garcke) Boiss. Only the uppermost leaves whorled or opposite; erect perennials, with entire leaves equal at base; stipules none; involucres mostly 5-lobed, in the forks of the branches and terminal¡ inflorescence umbelliform.

E. corollàta L. (FLOWERING S.) Glabrous or sometimes sparingly hairy, 4-10 dm. high; root deep; stem usually simple for more than half its length; leaves ovate, lanceolate, or linear, entire, obtuse; umbel 5(3-7)-forked, and the forks again 2-3(or rarely 5)-forked; involucres long-peduncled, with showy white appendages (appearing like petals), the lobes minute and incurved; pod slender-pediceled, smooth; seeds thick, 2 mm. long or more, ash-colored, slightly uneven. — Rich or sandy soil, N. Y. to Fla., w. to Minn, and La.; also locally naturalized in N. E. July-Oct.


Green Poinsettia (Euphorbia dentata)

There doesn’t seem to be much point to a green Poinsettia, but this one is not entirely green: it adds the subtly decorative touch of whitish markings on the upper leaves, no doubt to provide a more prominent target for insect pollinators. It may not be quite the spectacle that the Christmas Poinsettia is, but it’s a handsome plant if we view it with an indulgent eye.

This species, along with its more decorative sister E. pulcherrima, has been in and out of the genus Euphorbia. When botanists are feeling frisky, they split off the genus Poinsettia; then, the next morning, in a fit of remorse, they stuff the genus back into Euphorbia and hope nobody notices. Right now the consensus seems to be that Poinsettia is a subgenus or section of the gigantic genus Euphorbia. This is Gray’s view.

Gray describes the genus, the subgenus, and the species:

EUPHÓRBIA L. SPURGE. Flowers monoecious, included in a cup-shaped 4-6-lobed involucre (flower of older authors) resembling a calyx or corolla, and usually bearing large thick glands (with or without petal-like margins) at its sinuses. Sterile flowers numerous and lining the base of the involucre, each from the axil of a little bract, and consisting merely ol a single stamen Jointed on a pedicel like the filament; anther-cells globular, separate. Fertile flower solitary in the middle of the involucre, soon protruded on a long pedicel, consisting of a 3-lobed and 3-celled ovary with no calyx (or a mere vestige). Styles 3, each 2-cleft; the stigmas therefore 6. Pod separating into three 1-seeded carpels, which split, plastically into 2 valves. Seed often caruncled (ours only in §§ 5 and 6). — Plants (ours essentially herbaceous) with a milky acrid juice. Peduncles terminal, often umbellate-clustered; in the first section mostly appearing lateral, but not really axillary. (Named for Euphorbus, physician to King Juba.)

POINSÉTTIA (Graham) Baill. Involucres in terminal clusters, 4-5-lobed, with few (or often solitary) cup-shaped glands; erect annuals, with entire, dentate, or sinuate leaves, all or only the upper ones opposite, the uppermost often colored, especially at base; stipules reduced to small glands.

E. dentàta Michx. Erect or ascending, hairy, 2.5-12 dm. high; leaves ovate, lanceolate, or linear, petioled, coarsely toothed, 4-8 cm. long, only the lowest alternate, the upper often paler at base; involucres almost sessile, with 5 oblong dentate lobes, and one or sometimes more short-stalked glands; seeds ovoid-globular, slightly tubercled. — Rich soil, Pa. to Wyo. and Tex. July-Sept.


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