Asclepias L.

George R. Proctor (2012). Flora of the Cayman Isands (Second Edition). Royal Botanic Gardens, Kew

Morphology General Habit

Usually erect, perennial herbs; leaves opposite or whorled

Morphology Reproductive morphology Flowers

Flowers in umbels on axillary or terminal peduncles; calyx 5–10-glandular within at the base; corolla deeply 5-lobed, the lobes reflexed; scales of the corona 5, attached to the stamen-tube, erect and concave- hooded, ligulate within

Morphology Reproductive morphology Flowers Pollinia

Pollinia pendulous from apex of the anther-cell

Morphology Reproductive morphology Flowers Gynoecium Stigma

Stigma flat, 5- angled or obtusely 5-lobed

Morphology Reproductive morphology Seeds

Follicles acuminate, smooth or rarely spiny-tuberculate.

Distribution

A chiefly N. American genus of about 120 species.

Goyder, D.J. (2009). A synopsis of Asclepias (Apocynaceae: Asclepiadoideae) in tropical Africa. Kew Bulletin 64: 369. https://doi.org/10.1007/s12225-009-9133-3

Type

Type species: A. syriaca L. (lectotype designated by Hitchcock in Hitchcock & Green 1929: 136 (see also Jarvis 2007: 322)).

Morphology General Habit

Slender to robust perennial herbs with annual stems arising from a tuber or fleshy taproot; latex white; stems prostrate to erect, simple or branched

Morphology Leaves

Leaves opposite, linear to broadly ovate

Morphology Reproductive morphology Inflorescences

Inflorescences terminal or extra-axillary, nodding or erect, umbelliform, sessile or pedunculate

Morphology Reproductive morphology Flowers

Flowers 5-merous

Morphology Reproductive morphology Flowers Corolla

Corolla divided almost to the base, lobes campanulate, spreading or reflexed

Morphology Reproductive morphology Flowers Corona

Corolline corona absent

Morphology Reproductive morphology Flowers Gynostegium

Gynostegial corona of 5 generally cucullate fleshy lobes arising from the staminal column in a staminal position; minute interstaminal lobes sometimes also present

Morphology Reproductive morphology Flowers Pollinia

Pollinia pendant in anther cells; translator arms slender and terete or flattened, sometimes clearly geniculate, but never with a massively expanded proximal portion and slender distal portion

Morphology Reproductive morphology Flowers Gynoecium

Stylar head rarely projecting much beyond top of anthers (but long-rostrate in Asclepias longirostra)

Morphology Reproductive morphology Fruits

Follicles mostly single by abortion, generally held erect, smooth, occasionally ribbed or with lines of soft pubescent processes

Morphology Reproductive morphology Seeds

Seeds ovate, discoid, with a coma of silky hairs.

Distribution

A genus with two major centres of distribution, one New World with c. 120 spp mostly centred on southern parts of the North American continent, the other Old World, with c. 80 spp, 38 of these in tropical Africa with the remainder in southern Africa. In addition, many segregate genera have been recognised in the Old World. In the broad sense the Asclepias radiation comprises some 380 – 400 species.

Apocynaceae (part 2), David Goyder, Timothy Harris, Siro Masinde, Ulrich Meve, Johan Venter. Flora of Tropical East Africa, 2012

Morphology General Habit

Perennial herbs with annual stems arising from a tuber or fleshy taproot.

Morphology General Exudate

Latex white.

Morphology Stem

Stems prostrate to erect, simple or branched

Morphology Leaves

Leaves opposite

Morphology Reproductive morphology Inflorescences

Inflorescences terminal or extra-axillary, nodding or erect, umbelliform, sessile or pedunculate

Morphology Reproductive morphology Flowers

Flowers 5-merous. Corolla divided almost to the base, lobes campanulate, spreading or reflexed. Corolline corona absent

Morphology Reproductive morphology Flowers Corona

Gynostegial corona of 5 generally cucullate fleshy lobes arising from the staminal column in a staminal position; minute interstaminal lobes sometimes also present

Morphology Reproductive morphology Flowers Pollinia

Pollinia pendant in anther cells; translator arms slender and terete or flattened, sometimes clearly geniculate, but never with a massively expanded proximal part and slender distal part.

Morphology Reproductive morphology Flowers Gynoecium Style

Stylar head rarely projecting much beyond top of anthers (but long-rostrate in A. longirostra)

Morphology Reproductive morphology Fruits

Follicles mostly single by abortion, generally held erect, smooth, occasionally ribbed or with lines of soft pubescent processes

Morphology Reproductive morphology Seeds

Seeds ovate, discoid, with a coma of silky hairs.

Note

In addition, many segregate genera have been recognised in the Old World. In the broad sense the Asclepias radiation comprises some 380–400 species. Molecular surveys of this group do not lend support to current generic delimitations (see Goyder et al. in Ann. Missouri Bot. Gard. 94: 423–434, 2007 and Fishbein et al. in Syst. Bot. 36: 1008–1023, 2011). However, they do not suggest a workable alternative, so the morphologically distinctive African segregate genera Margaretta, Stathmostelma, Gomphocarpus, Pachycarpus, Xysmalobium and Glossostelma have been maintained in this treatment. I can only echo N.E. Brown’s view on the subject published in his openly artificial treatment of the group for the F.T.A. 4(1): 299 (1902): “Undoubtedly Xysmalobium, Asclepias and Schizoglossum are but artificial divisions of one natural genus, since they cannot be separated by characters that do not break down at some point…” but he then goes on to say how he has allocated species to each. We have moved on considerably since then in recognising more natural units, but the phylogenetic structure is still inadequate for a stable reallignment of the group at generic level.