Seddera repens Hallier

Deroin, Thierry & Demissew, Sebsebe, 2009, The genus Seddera Hochst. (Convolvulaceae) in Madagascar, Adansonia (3) 31 (1), pp. 207-214 : 211-214

Seddera repens Hallier f.

( Fig. 2 )

Bulletin de l’Herbier Boissier 6: 530 (1898).

MATERIAL EXAMINED. — Madagascar. Province deToliara, environs de Tuléar, delta du Fiherenana , alt. 2-10 m, 14- 26.IX.1924, Humbert & Perrier de la Bâthie 2447 ( G, P) . — Delta de la Linta (côte sud-ouest), alt. 1-10 m, 24-28.VIII.1928, Humbert & Swingle 5481 ( P) . — Bassin de la Malio (affluent du Mangoky), près d’Ambalabe , alt. 400-500 m, 23-27.XI.1946, Humbert 19334 ( P) . — D’Ampanihy à l’embouchure de la Menarandra (extrême sud), alt. 1-200 m, 10-11.III.1955, Humbert & Capuron 29352 ( P) . — 5 km au N de Befotaka [most probably Ifotaka] ( Mandrare ), IV.1960, Keraudren 1005 ( P) . — SW of Ifotaka , 17.XI. 1938, Lam & Meeuse 5426 ( K) . — Sud-Est, entre Imonty et Amboasary , 7.XII.1960, Leandri 4344 ( P) . — Route nationale 27, km 40 [35 km SSE from Ihosy], 21.XII.1965, Peltier 5577 ( P) . — Bassin de l’Onilahy , III.1910, Perrier de la Bâthie 9129 ( P) . — Sud-Ouest, Manampetsa [Lake Tsimanampetsotsa], IV.1933, Perrier de la Bâthie 19053 ( P) . — Beza Mahafaly Reserve, near Betioky, Parcelle 2, 6.I.1988, Phillipson 2816 ( K, MO) . — Province de Mahajanga, env. de Majunga , alt. 2-15 m, 28-30.XII.1924, Humbert 4058 ( G, K, P) . — Nosy Be , 12.III.1878, Rutenberg s.n. (holo-, CSR, not seen) .

DESCRIPTION

Shrublet 15-30 cm high. Branches thin and slen- der, pubescent. Leaves subsessile; lamina elliptic to suborbicular, 4-11 × 3-7 mm; retuse, acute and mucronulate at the apex, rounded to subcuneate at the base, hirsute; petiole 1-2.5 mm long. Inflorescence axillary, solitary, with 1 or 2-3 flowers; peduncle absent to 1-5 (-17) mm long; pedicel 1-1.5 mm long; bracts linear 1-1.5 mm long. Sepals 5, unequal; 3 outer ones elliptic 5-6 × 1.5-2 mm, 2 inner ones ovate-lanceolate, broader at the base 4.5 × 1-1.5 mm, all acute at the apex. Corolla white, occasionally blue (Phillipson 2816), 5-6 mm long, pubescent on mid-petaline areas. Stamens 5, ± equal with filaments 3-3.3 mm long; anthers 0.7 mm long. Ovary pubescent in the upper half, long ovoid; styles 2, 3- 3.2 mm long, with capitate stigma. Fruit 4-valved, 4-seeded, c. 2.5-3 mm long, hairy at the apex. Seeds black, 1.5-2 mm long.

ECOLOGY

Xerophyllous bush at low altitudes.

DISTRIBUTION ( Fig. 3 )

Known only from Madagascar, in the Mahafaly and Androy territories, like S. madagascariensis , but also in Isalo (Malio basin), near Ihosy, and in the west (Majunga basin) and north (Nosy Be island), equally on siliceous or carbonated soils. It is hardly conceivable the distribution is so scattered, more collections in the future of this relatively neglected species may fill the gaps between the known localities.

CONSERVATION STATUS

Restricted to the western part of Madagascar, Seddera repens has an EOO of c. 225 000 km2, an AOO of 1100 km 2, and c. 11 subpopulations now recognized, two of which are encompassed within protected areas (Tsimanampetsotsa, Beza Mahafaly Reserve). Using the IUCN Red List threat criteria ( IUCN 2001), it might be assigned a preliminary status of Least Concern (LC).

FLOWERING TIME

Flowering has been recorded from September to April. Phenology is very like that of S. madagascariensis , no flowering collections are known from May to August, the peak of the dry season.

MORPHOLOGICAL REMARKS

AND CONCLUSIONS

The two species are similar to each other, as the main differences are in the relative proportions of reproductive parts. The restricted distribution of Seddera madagascariensis suggests a speciation from S. repens on limestone soils, and under more severe dry conditions. Field observations are needed to ascertain whether or not the two species may hybridize in the Mahafaly and Androy territories.

The most distinctive feature of S. madagascariensis is the unilocular ovary, until now unknown in Seddera . This situation shows a striking similarity with that in another Convolvulaceae of Madagascar, Bonamia ankaranensis Deroin (2004) , in which the ovary is bilocular in the youngest ontogenetical stages, but the septum vanishes at anthesis, and the mature fruit is 1-seeded. In the genus Bonamia , styles are usually separate too. As we also failed to see a septum in S. repens ( Fig. 2O ) – Hallier (1898) describing only a “ saepto pellucido membranaceo ” in the dehiscing capsule – it is most probable that, unlike Seddera in mainland Africa, Malagasy species have reduced or resorbed ovarian septa at the anthesis, with a trend to monospermy. Such an ontogenetical acceleration in the gynoecium morphogenesis has already been recognized in the family, especially in Ipomoeae ( Deroin 1999).

Due to the new information generated, it is important to amend the generic key (in French)

Figures

FIG. 2. — Seddera repens Hallier f.: A, habit with rosette base;B, flowering branchlet;C, D, leaf (abaxial and adaxial sides respectively); E, floral bud;F, G, bracts;H-L, sepals (from outside to centre);M, corolla opened showing androecium and gynoecium;N, pollen grain; O, ovary (lengthwise section); P, dehiscing capsule surrounded by the calyx; Q-S, seed (adaxial and lateral sides,lengthwise section). Humbert & Swingle 5481. Drawn by Thierry Deroin. Scale bars: A, 1 cm; B-D, P, 5 mm; E-M, O, Q-S, 1 mm; N, 50 μm.

FIG. 3.— Distribution of Malagasy Seddera species:A, S. madagascariensis Deroin & Sebsebe;B, S. repens Hallier f. (phytogeographical frame after Humbert 1955).