Acanthospermum

Schrank

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

Etymology: Greek acantha, prickle, and sperma, seed, alluding to prickly “fruits”
Found in FNA Volume 21. Treatment on page 36. Mentioned on page 33.
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
Facts about "Acanthospermum"
AuthorJohn L. Strother +
EtymologyGreek acantha, prickle, and sperma, seed, alluding to prickly “fruits” +
IllustratorBarbara Alongi +
Referenceblake1921a +
Taxon nameAcanthospermum +
Taxon parentAsteraceae (tribe Heliantheae) subtribe Melampodiinae +
Taxon rankgenus +
VolumeVolume 21 +