Mirabilis albida (Walter) Heimerl

White Four-o'Clock


CC = 5
CW = 5
MOC = 73

© SRTurner

Family - Nyctaginaceae

Habit - Perennial forb with woody roots.

Stems - Erect, to 1.0 m, glabrous to densely hairy, the hairs often in 2 vertical bands, when hairy sometimes also glandular, when glabrous appearing light brown, tan or silvery-whitened.

Mirabilis_albida_stem.jpg Stem and node.

© SRTurner

Mirabilis_albida_stem2.jpg Stem detail showing vertical band of hairs.

© SRTurner

Leaves - Opposite, simple, entire, sessile or with a short petiole less than 1 cm. Blades 3-10 cm long, linear to more commonly lanceolate or oblong-elliptic, rarely narrowly ovate, narrowed or tapered at the base, narrowed or abruptly tapered to a rounded or bluntly pointed (rarely sharply pointed) tip, glabrous to densely hairy, sometimes also somewhat glandular, when glabrous the undersurface pale or glaucous.

Mirabilis_albida_leaves1.jpg Stem and leaf node.

© SRTurner

Mirabilis_albida_leaf1.jpg Leaf adaxial.

© SRTurner

Mirabilis_albida_leaf2.jpg Leaf abaxial.

© SRTurner

Inflorescences - Terminal and axillary, or sometimes only axillary. Flower clusters with 2-5 flowers, subtended by a calyxlike involucre of fused bracts. Involucre 4-5 mm long at flowering, glabrous or sparsely to densely hairy on the surfaces, sometimes also glandular, becoming enlarged to 8-12 mm long at fruiting, broadly bell-shaped at maturity, with 5 broad shallow lobes, persistent, somewhat flattened, and somewhat papery at fruiting.

Mirabilis_albida_inflorescence1.jpg Inflorescence.

© SRTurner

Mirabilis_albida_inflorescence2.jpg Inflorescence.

© SRTurner

Flowers - Perfect, actinomorphic, rarely seen fully expanded. Calyx 6-10 mm long, 5-lobed, white to pink, the expanded portion bell-shaped to saucer-shaped at flowering, the lobes notched at the tip. Petals absent. Stamens 1-5, the filaments free or sometimes fused into a ring at the base, the anthers attached basally. Pistil 1 per flower, the ovary superior but appearing inferior because of the closely enveloping perianth tube, consisting of 1 carpel, with 1 locule, the placentation basal. Style 1, the stigma globose or disclike. Ovule 1.

Mirabilis_albida_flower.jpg Involucre and flower. Flowers in this species are rarely seen fully expanded.

© SRTurner

Fruits - Achenes surrounded by the persistent, hardened or somewhat fleshy perianth tube, 4-6 mm long, noticeably warty on the angles and sides, each tubercle of the angles with a tuft of short hairs at the tip, otherwise minutely hairy, olive green to dark brown.

Mirabilis_albida_fruit1.jpg Involucre with fruits.

© SRTurner

Mirabilis_albida_fruit2.jpg Fruits.

© SRTurner

Flowering - May - October.

Habitat - Upland prairies, sand prairies, glades, tops and ledges of bluffs, streambanks, upland forest openings, pastures, roadsides, railroads, open disturbed areas.

Origin - Native to the U.S.

Lookalikes - M. nyctaginea, which is more common.

Other info. - This inconspicuous species is found in most counties south of the Missouri River, less commonly in the north. Its range in the continental U.S. is somewhat unusual, comprising a broad north-south band through about the center third of the country. The plant is recognized by its unusual persistent involucres, which are papery and contain the tiny fruits at their centers (though these are easily dislodged). The whitened involucres are sometimes believed to be the flowers, and are probably responsible for the somewhat deceptive common name. The plant is differentiated from the more common M. nyctaginea by its leaves. Leaves of M. nyctaginea are broader, with longer and well-defined petioles. The fruits are also different, with those of M. albida being noticeably warty on the angles (use magnification to see this clearly)

Flowers of plants in this genus do not have petals. The showy parts are the calyces, which are bright pink; however, these are not often seen in fully extended form. The common term "four o'clock" refers to the observation that the flowers are open only in the late afternoon. However, this trait is highly variable.

Photographs taken at Sand Prairie Conservation Area, Scott County, MO, 8-15-2021 (SRTurner).