Herbs or subshrubs, annual or perennial, caulescent, glaucous, from transitory or persistent taproots; sap white to orange. Stems leafy, branching. Leaves sessile; basal rosulate, cauline alternate; blade unlobed or commonly shallowly to deeply 1×-lobed; margins dentate, each tooth terminated by prickle; surfaces glaucous, often mottled over veins, unarmed or prickly, glabrous or hispid. Inflorescences terminal, cymose; bracts present. Flowers conspicuous, sometimes subtended by foliaceous bracts; sepals 2 or 3, unarmed or prickly, each with erect, subterminal, hollow horn tipped with prickle; petals 6, in 2 whorls of 3; stamens 20-250 or more; pistil 3-5(-7)-carpellate; ovary 1-locular; style short, to 3 mm in fruit; stigma 3-5(-7)-lobed. Capsules erect, 3-5(-7)-valved, grooved over sutures, prickly, rarely unarmed, dehiscing from apex ca. 1/3 length, valves separating from framework of vascular elements, to which persistent style and stigma remain attached. Seeds numerous, subglobose, minutely pitted, 1-3 mm, aril present. x = 14.
North America, South America, Hawaii, introduced in other tropical and temperate regions of the world.
Species 32 (15 in the flora).
None of the North American species occurs in South America except for the pantropical weeds Argemone mexicana and, probably, A. ochroleuca. Argemone glauca is endemic to Hawaii. Three suffrutescent, perennial species are known from Mexico in Coahuila (A. fruticosa) and Chihuahua (A. turnerae, A. ownbeyana).
Most herbaceous species can be hybridized, but the F1 plants are sterile when the parents differ in ploidy level. The F2 generation, when achieved, consists mainly of plants of low vigor.
The alkaloids of Argemone have been studied extensively. F. S. Stermitz (1968) has suggested that the species fall into four groups (one with two subgroups) according to their alkaloidal properties, and that these groups coincide to a considerable degree with the informal species alliances suggested by G. B. Ownbey (1958). A full evaluation of the importance of alkaloidal content to Argemone taxonomy and evolution has not been published, but there is little doubt that it is highly significant.
The name Argemone intermedia Sweet (Hort. Brit. ed. 2, 1830) is encountered in several regional and local floras but is of uncertain application.
|1||Petals yellow, golden, or bronze.||> 2|
|1||Petals white or pale lavender.||> 4|
|2||Stamens 150 or more, filaments red or purplish; flowers 7–12 cm wide; petals bright yellow to golden or bronze.||Argemone aenea|
|2||Stamens 20–75, filaments yellow; flowers 3–7 cm broad; petals pale lemon yellow to bright yellow.||> 3|
|3||Flower buds subglobose, body length ± equal to breadth; petals mostly bright yellow.||Argemone mexicana|
|3||Flower buds oblong, body length 1.5–2 times breadth; petals mostly pale lemon yellow.||Argemone ochroleuca|
|4||Leaf surfaces prickly on veins, often also minutely prickly or hispid between veins; stems usually closely prickly.||> 5|
|4||Leaf surfaces rarely prickly except on veins or unarmed; stems with widely spaced prickles or almost unarmed (copiously long-prickly in A. arizonica).||> 9|
|5||Longest capsular prickles simple, 5–8(–10) mm.||> 6|
|5||Longest capsular prickles branched, usually 8–35 mm.||> 7|
|6||Distal leaf blades not clasping; leaf surfaces densely crisped-hispid between main veins.||Argemone hispida|
|6||Distal leaf blades usually definitely clasping; leaf surfaces variously prickly but not crisped-hispid.||Argemone munita|
|7||Longest capsular prickles 15–35 mm.||Argemone aurantiaca|
|7||Largest capsular prickles about 8–15 mm.||> 8|
|8||Apices of leaf lobes angular, marginal teeth 3 mm or more; flowers usually closely subtended by 1–2 foliaceous bracts.||Argemone squarrosa|
|8||Apices of leaf lobes usually definitely rounded, marginal teeth usually less than 1 mm; flowers usually not closely subtended by foliaceous bracts.||Argemone munita|
|9||Longest capsular prickles branched, usually 8–35 mm.||> 10|
|9||Longest capsular prickles simple, 4–10(–12) mm.||> 11|
|10||Longest capsular prickles 15–35 mm.||Argemone aurantiaca|
|10||Longest capsular prickles 8–15 mm.||Argemone squarrosa|
|11||Prickles (when present) of sepals and sepal horns ascending, or sepals unarmed; blades of proximal leaves often lobed less than 1/2 distance to midrib.||> 12|
|11||Prickles (when present) of sepals and sepal horns patent; blades of proximal leaves mostly lobed more than 1/2 distance to midrib.||> 17|
|12||Leaf blades thick and leathery; stamens 100–120.||Argemone corymbosa|
|12||Leaf blades often succulent, but not leathery; stamens 150 or more.||> 13|
|13||Flower buds obovoid or oblong; sepal horns usually flattened adaxially.||> 14|
|13||Flower buds usually subglobose, rarely ellipsoid or ellipsoid-oblong; sepal horns terete.||> 15|
|14||Flower buds obovoid; surface of sepal horns prickly; blades of proximal leaves lobed ca. 3/4 distance to midrib, apices of lobes angular, marginal teeth prominent.||Argemone pleiacantha|
|14||Flower buds oblong; surface of sepal horns unarmed; blades of proximal leaves lobed ca. 1/2 distance to midrib, apices of lobes rounded, marginal teeth very short.||Argemone munita|
|15||Distal leaves not evidently clasping; stems with scattered prickles, the longest 7–10 mm.||Argemone gracilenta|
|15||Distal leaves clasping; stems with shorter prickles.||> 16|
|16||Sepal horns 6–10(–15) mm; flower buds ellipsoid-oblong; capsules narrowly to broadly ellipsoid.||Argemone polyanthemos|
|16||Sepal horns 3–6(–10) mm; flower buds subglobose to broadly ellipsoid; capsules oblong to oblong-ellipsoid or narrowly ellipsoid.||Argemone albiflora|
|17||Blades of distal leaves usually definitely clasping; blades of proximal leaves lobed ca. 1/2–3/4 distance to midrib.||> 18|
|17||Blades of distal leaves not definitely clasping; blades of proximal leaves lobed 4/5 distance to midrib or more.||> 19|
|18||Blades of proximal leaves lobed ca. 3/4 distance to midrib, apices of lobes angular.||Argemone pleiacantha|
|18||Blades of proximal leaves lobed 1/2 or less distance to midrib, apices of lobes usually rounded.||Argemone munita|
|19||Flower buds usually subglobose; sepal horns terete, usually slender, unarmed.||Argemone gracilenta|
|19||Flower buds oblong to obovoid or ellipsoid; sepal horns terete or flattened or angular, usually prickly.||> 20|
|20||Stems copiously long-prickly, often decumbent, diffusely branched; blades of basal and proximal leaves lobed nearly to midrib, lobe length often 5 times width; sepal horns 12–15 mm.||Argemone arizonica|
|20||Stems sparsely to copiously prickly, erect, not diffusely branched; blades of basal and proximal leaves lobed 4/5 distanct to midrib or less, lobes proportionately broader; sepal horns 5–12 mm.||> 21|
|21||Flower buds usually oblong-obovoid, rarely subglobose; sepal horns usually flattened adaxially, rarely terete.||Argemone pleiacantha|
|21||Flower buds broadly ellipsoid to ellipsoid-oblong; sepal horns terete or angular.||> 22|
|22||Stems often closely prickly; capsules narrowly ellipsoid-ovoid; seeds 1.8–2.2 mm.||Argemone chisosensis|
|22||Stems not closely prickly; capsules narrowly to broadly ellipsoid; seeds about 1.5 mm.||Argemone sanguinea|