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Pakistan | Family List

Asclepiadaceae

S.I. ALI


Department of Botany, University of Karachi, Karachi.

Caralluma edulis
Illustration

Credit: Surayya Khatoon

Erect, creeping, scrambling or twining herbs and shrubs, sometimes succulent, usually with milky latex. Leaves opposite, simple, sometimes reduced or absent, exstipulate, entire. Flowers actinomorphic, bisexual, 5-meous, in terminal or lateral umbelloid, corymbose or paniculate cymes. Sepals united, shortly connate or almost free, imbricate. Corolla gamopetalous, rotate, campanulate, tubular, lobes valvate or twisted in bud, rarely imbricate. Stamens 5, epipetalous, alternating with corolla lobes, either connivent by the anthers (Periplocoideae) or completely connate and adnate to the style apex forming a gynostegium (Asclepiadoideae). Corona of one or two series, attached to the corolla or to the staminal column or the outer series to the corolla and the inner to the staminal column. Anthers longitudinally dehiscent or opening by terminal slits. In Periplocoideae the pollen grains are in tetrads and fall into spatulate pollen carriers with adhesive disc formed on the surface of the style apex between the anthers. In Asclepiadoideae 1 or 2 pollinia (waxy masses) per anther locule are present; the pollinia of adjacent locules of adjacent anthers are connected by the translator apparatus, which consists of a corpusculum and two arms or retinaculae, each of which bears a pollinium. Carpels 2, superior, united only by the enlarged style apex, multiovulate, placentation parietal. Fruit of 2 distinct or single (by abortion) follicles. Seeds flattened, without an aril, comose.

A family with 175-180 genera and 2200 species (Willis, Dict. Fl. Pl. Ferns, 98.874. 1973) distributed mainly in the tropical and subtropical regions of the world; represented in Pakistan by 23 genera and 41 species. Opinion seems to be divided about segregating Periplocaceae from Asclepiadaceae. For instance Bullock (in Hutchinson & Dalziell, Fl. Trop. Afr. ed. 2. 2:81. 1963) and Huber (in Abeywickrama, Fl. Ceylon 1:28. 1973) have treated the two as independent families, whereas, more recently, Markgraf (in Tutin et al., Fl. Europ. 3:70. 1972) Rechinger f. (Fl. Iran. 73: 1. 1973), Spellman (in Ann. Miss. Bot. Gard. 62:103, 108. 1975) and Stevens (in Saldanha & Nicolson, Fl. Hassan Distr. 437. 1976) have taken a broader view and have accepted the family Asclepiadaceae including the subfamily Periplocoideae. We have also accepted the family in a broader sense.

i) Subfamily Asclepiadoideae

a. Tribe Asclepiadeae : Asclepias, Calotropis, Cynanchum, Glossonema, Holostemma, Oxystelma, Pentatropis, Pergularia, Sarcostemma, Vincetoxicum.

b. Tribe Marsdenieae : Hoya, Marsdenia, Telosma, Tylophora, Wattakaka.

c. Tribe Ceropegieae : Caralluma, Ceropegia, Leptadenia, Orthanthera.

ii. Subfamily Periplocoideae

Tribe Periploceae : Cryptolepis, Cryptostegia, Hemidesmus, Periploca.

Acknowledgements: I am grateful to the authorities of the following herbaria for herbarium and library facilities: Royal Botanic Gardens, Kew; British Museum (Natural History), London and National Herbarium, Islamabad. I am indebted to Mr. B.L. Burtt, Mr. I.C. Hedge (Edinburgh) and Mr. David Field (Kew) for going through the manuscript and offering suggestions for its improvement. I am thankful to Miss Surayya Khatoon who has kindly executed some of the illustrations. The financial assistance received from the United States Department of Agriculture under P.L. 480 with the coordination of the Pakistan Agricultural Research Council, Islamabad, is thankfully acknowledged.


1 Plant cactus-like, stem thick fleshy   16 Caralluma
+ Plant not cactus-like   (2)
       
2 (1) Plants erect   (3)
+ Plants climbing or scrambling   (11)
       
3 (2) Filaments usually free; anthers acuminate or with a terminal appendage; pollen masses granular, in pairs in each cell   23 Periploca
+ Filaments connate, pollen masses waxy   (4)
       
4 (3) Anthers an expanded membranous tip; pollen masses waxy (pollinia), solitary in each cell (10 in all) sessile or pedicelled in pairs on corpuscule, pendulous (Tribe Cynancheae)   (5)
+ Anthers incumbent on the stigma, without a membranous tip; pollen masses one in each cell (10 in all) sessile in pairs on the corpuscule   (10)
       
5 (4) Corona double or with appendages on the inner face   3 Cynanchum
+ Corona single, without appendages on the inner face   (6)
       
6 (5) Follicles echinate   4 Glossonema
+ Follicles smooth   (7)
       
7 (6) Generally a leafless shrub or leaf (when present) 6-7 mm long   23 (P. aphylla)
+ Plants with normal leaves   (8)
       
8 (7) Corolla lobes twisted   10 Vincetoxicum
+ Corolla lobes valvate   (9)
       
9 (8) Coronal processes laterally compressed; shrub or small tree, leaf base cordate   2 Calotropis
+ Coronal processes spathulate; herb, leaf base tapering   1 Asclepias
       
10 (4) Calyx turbinate, 5-lobed, corolla rotate   18 Leptadenia
+ Calyx 5-partite, corolla salver-shaped   19 Orthanthera
       
11 (2) Filaments usually free; anthers acuminate or with a terminal appendage; pollen masses granular, in pairs in each cell   (12)
+ Filaments connate into a tube; pollen masses waxy   (15)
       
12 (11) Coronal scales connate into a lobed ring   23 Periploca
+ Coronal scales corolline, free, short, thick   (13)
       
13 (12) Corolla lobes valvate (corolla rotate)   22 Hemidesmus
+ Corolla lobes twisted or imbricate   (14)
       
14 (13) Corolla 10-14 mm long, rotate   20 (C.buchananii)
+ Corolla 5-6 cm long, funnel-shaped   21 (C. grandiflora)
       
15 (11) Anthers with a membranous appendage   (16)
+ Anthers incumbent on the style-apex without a membranous appendage   17 Ceropegia
       
16 (15) Pollen masses pendulous (1 in each cell, 10 in all)   (17)
+ Pollen masses erect, rarely horizontal (never pendulous)   (24)
       
17 (16) Corona double   (18)
+ Corona single   (21)
       
18 (17) Follicles echinate   8 Pergularia
+ Follicles smooth   (19)
       
19 (18) Trailing leafless shrub   9 Sarcostemma
+ Twinning leafy shrub or herb   (20)
       
20 (19) Corona tips curved over stigma; corolla divided half way down   6 Oxystelma
+ Corona tips not as above; corolla divided more than half its length   3 Cynanchum
       
21 (17) Corona 5-lobed   (22)
+ Corona 10-lobed   (23)
       
22 (21) Corona segment produced at the base into a spur and the apex into a slender tip   7 Pentatropis
+ Corona segment without a spur, the apex not as above   10 Vincetoxicum
       
23 (21) Corolla> 10 mm long (in our species)   5 Holostemma
+ Corolla 5 mm or less long   3 Cynanchum
       
24 (16) Corolla lobes twisted   (25)
+ Corolla lobes valvate   11 Hoya
       
25 (24) Corona lobes tubercle-like and entirely adnate to the staminal column or radiating from its base   14 Tylophora
+ Corona lobes with their basal part adnate to the staminal column, shortly free above   (26)
       
26 (25) Corona lobes without a process on the inner face of their free apical part   12 Marsdenia
+ Corona lobes with an apical tooth or an appendage arising from the inner face   (27)
       
27 (26) Corona lobes with the free part expanded and with a linear appendage arising from the inner face; corolla tube inflated at the base   13 Telosma
+ Corona lobes with an apical tooth projecting horizontally inwards; corolla tube not inflated at the base   15 Wattakaka

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