Acanthospermum

Schrank

Pl. Rar. Hort. Monac. 2: plate 53. 1820.

Etymology: Greek acantha, prickle, and sperma, seed, alluding to prickly “fruits”
Treatment appears in FNA Volume 21. Treatment on page 36. Mentioned on page 33.
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Annuals (sometimes persisting), 10–60(–120) cm. Stems erect to ± prostrate (repeatedly “forked”). Leaves cauline; opposite; petiolate or ± sessile; blades mostly elliptic to deltate, rhombic, or ovate, sometimes lyrate, ultimate margins entire or toothed, faces usually pilosulous to sericeous or scabrellous, sometimes glabrate or glabrescent, usually gland-dotted. Heads radiate, 1(–3) in “forks” of branches (terminal, appearing axillary by sympodial growth). Involucres ± hemispheric, 3–5 mm diam. (becoming ± rotate in fruit). Phyllaries persistent (outer) or falling, 10–13 in 2 series (outer 4–6 herbaceous, inner 5–8 each investing a ray ovary, enlarging in fruit to form a perigynium, shed with enclosed cypsela). Receptacles convex, paleate (paleae cuneate to spatulate, ± conduplicate or flattish, membranous). Ray florets 5–8, pistillate, fertile; corollas yellowish (tubes shorter than to equaling laminae, laminae ovate to elliptic or linear). Disc florets 3–8(–12+), functionally staminate; corollas yellowish, tubes shorter than funnelform or campanulate throats, lobes 5, deltate. Cypselae each enclosed within and shed with an often hardened, ± prickly perigynium (the ultimate “fruits” plumply ellipsoid to fusiform, or ± compressed); pappi 0 or rudimentary. x = 11.

Distribution

Introduced; mostly tropical to warm-temperate New World, also introduced in Old World.

Discussion

Species 6 (3 in the flora).

Key

1 Fruits 7–9+ mm, 5–7-ribbed, terminal spines 0 Acanthospermum australe
1 Fruits 2–6 mm, 3-ribbed or not notably ribbed, terminal spines 2 > 2
2 Leaf blades rhombic-ovate to obovate, (20–)40–120(–150+) mm; fruits not notably ribbed, prickles ± scattered Acanthospermum hispidum
2 Leaf blades ovate to lyrate, 10–30(–45) mm; fruits usually 3-ribbed, prickles mostly along 2 ribs and around apices Acanthospermum humile
... more about "Acanthospermum"
John L. Strother +
Schrank +
mostly tropical to warm-temperate New World +  and also introduced in Old World. +
Greek acantha, prickle, and sperma, seed, alluding to prickly “fruits” +
Pl. Rar. Hort. Monac. +
blake1921a +
Compositae +
Acanthospermum +
Asteraceae (tribe Heliantheae) subtribe Melampodiinae +