Mirabilis nyctaginea
Mirabilis sect. Oxybaphus
four-o'clock, heart-leaf four-o'clock, heart-leaf umbrella-wort, heartleaf umbrellawort four-o'clock, umbrellawort, wild four-o'clock
usually erect or ascending, occasionally decumbent, leafy mostly in proximal 2/3 of plant, openly forked distally, 4–15 dm, basally usually glabrous or puberulent in 2 lines, rarely spreading-pubescent; distally stems usually puberulent in 2 lines, occasionally glabrate, rarely spreading glandular-pubescent.
erect to decumbent, sparsely to densely leafy primarily in proximal 2/3 or throughout.
ascending at 45–80°, abruptly reduced to inflorescence;
petiole 0.2–2 cm;
blade green, ovate-lanceolate to ovate or triangular, 3–10 × 2–6.5 cm, usually ± thin, base obtuse, round, truncate, or cordate, apex acute to acuminate, rarely rounded, surfaces usually glabrous, sometimes puberulent or sparsely hispidulous.
basal leaves petiolate, blade proportionately broader;
distal leaves sessile or subsessile, blade narrower, margins entire to crisped.
terminal and in upper axils, subumbellate clusters at ends of long, forked branches;
peduncle 5–20 mm, usually pubescent with ascending, often curved, glandular or eglandular hairs, crosswalls of hairs pale;
involucres pale green, often tinged pinkish, widely bell-shaped to almost rotate, 4–6 mm in flower, 8–15 mm in fruit, glabrous or glabrate but with minute curved hairs on margins, or rarely puberulent or pilose throughout, 50–90% connate, lobes ovate to broadly ovate.
axillary and terminal in open or congested, few or repeatedly branched cymes (single in axils, especially in cleistogamous phases);
involucres usually notably accrescent, becoming tan, translucent, prominently net-veined, broadly bell-shaped to saucer-shaped, with (1–)3 flowers inserted at base.
(2–)3(–5) per involucre;
perianth usually pink to reddish purple, rarely white, 1 cm.
perianth broadly funnelform, abruptly flared from narrow tubes, deeply 5-lobed;
stamens 3–5.
dark grayish brown to reddish brown (ribs and tubercles usually slightly paler), narrowly obovate and tapering at both ends, 3.4–5 mm, shaggy-pubescent with spreading, sometimes tufted, hairs, 0.3–0.4 mm, sometimes also with layer of minute hairs;
ribs usually irregularly and deeply notched, especially toward apex, round to bluntly angled, 0.5–0.75 times width of sulci, 0.5–1 times as wide as high;
sulci with pale small to tall tubercles that are sometimes horizontally lengthened and shelflike.
with 5 low ribs, obovoid or narrowly obovate and tapering at both ends, base prominently constricted, apex rounded to nipplelike, surface of fruit slightly rugose to prominently tuberculate on ribs and/or sulci (or ribs and/or sulci without tubercles), glabrous or pubescent, mucilaginous when wetted.
= 58.
Mirabilis nyctaginea
Mirabilis sect. Oxybaphus
Mirabilis nyctaginea is considered a noxious weed in some states. The holotype of Mirabilis ×collina Shinners is a hybrid between M. nyctaginea and M. albida. On the Great Plains, M. nyctaginea also appears to intergrade with M. albida. Prominence of the tubercles and redness of the fruits decreases in western populations. Near the Great Lakes, comparatively narrow-leaved plants with sparsely hirsute stems seem to be intergrades between M. nyctaginea and more or less hirsute M. albida. Mirabilis ×serotina Shinners is a hybrid between M. nyctaginea and M. glabra.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Species ca. 25 (10 in the flora).
Mirabilis sect. Oxybaphus is most diverse in the warm, semiarid regions of North America. Of all the subgroups (i.e., genera in P. C. Standley 1918) within a broadly constructed Mirabilis, sect. Oxybaphus has been the last to be maintained at the generic level by some authors of regional floras. The markedly accrescent involucres of most species make members of the section easily recognized. Standley (1931), in making transfers from Allionia and Oxybaphus to Mirabilis, noted that characteristics supposedly distinctive between segregate genera are not so in South America. C. F. Reed (1969) also used this justification for an inclusive Mirabilis in a treatment of Texas species.
Taxonomy at the species level within the section is unusually problematic. In the introduction to his treatment for Mirabilis, L. H. Shinners (1951b) expressed biological and nomen-clatural problems that plague satisfactory classification. R. W. Cruden (1973) showed cleistogamic and chasmogamic flowers in M. nyctaginea, and self-compatibility in chasmogamic flowers, and R. Spellenberg (1998) mentioned other biological attributes that probably contribute to difficulties. The floral mechanism that Cruden described for M. nyctaginea (stamens and style curling together as the flowers close in late morning) is found in all species and ensures self-pollination. Cleistogamic flowers are found in many other species. Chasmogamic flowers are attractive in some species and are visited by various strong-flying pollinators, among them bees and hummingbirds. B. L. Turner (1993b) used the argument of cleistogamy and hybridization, combined with phenotypic plasticity, to support his concept of a widespread and variable M. albida. Ultimately, some species complexes in the section may be treated more satisfactorily with a number of broadly distributed and variable species, each consisting of a number of infraspecific taxa.
Each species in this section intergrades in some respect with one or more others. Populations of these intergradient types are often highly uniform within. Here, insofar as practicable, species are recognized on combinations of characters that occur within some reasonably extensive geographic region and/or are found in populations that occur in certain rather well-defined ecological situations. Areas of difficult variation are the mountains of the south-western United States and the eastern base of the Rocky Mountains.
Measurements for leaves in the following descriptions are for leaves from mid-stem area. Leaves located toward the base are commonly proportionately broader and on longer petioles; those near and in the inflorescence are proportionately narrower and have much shorter petioles or are sessile.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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