Secamone clavistyla T.Harris & Goyder

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

Morphology General Habit

Slender woody twiner with white latex.

Morphology General Shoots

Young shoots pubescent with spreading reddish hairs; older stems glabrous

Morphology Leaves

Leaves with petiole 0.2–0.4 mm long, densely reddish-pubescent; lamina narrowly ovate to elliptic, rarely linear or ovate, 0.7–1.8 × 0.2–0.6 cm, apex apiculate, base rounded, lower surface sparsely pubescent, the surface ± smooth, the stomata not obscured by minute papillae, upper surface smooth and glabrous; red hairs restricted to upper and lower midrib

Morphology Reproductive morphology Inflorescences

Cymes mostly terminal, single-flowered; peduncle 0–1 mm long, glabrous.

Morphology Reproductive morphology Flowers Pedicel

Pedicels 2–3.5 mm long, glabrous

Morphology Reproductive morphology Flowers Calyx

Calyx lobes ovate to broadly ovate, 1 × 0.6 mm, apex rounded, margins ciliate

Morphology Reproductive morphology Flowers Corolla

Corolla 3–4 mm long, yellowish-green, divided for 1/2– 2/3 of its length; tube 0.5–1 mm long; lobes ovate-oblong, 1.9–3 mm long, apex rounded.

Morphology Reproductive morphology Flowers Corona

Corolline corona of 5 fleshy ridges from the base of the corolla tube and bifurcating around the corolla lobe sinuses

Morphology Reproductive morphology Flowers Androecium Stamens

Staminal corona lobes ± 0.5 × 0.1–0.2 mm, somewhat fleshy, adnate to the column from its base to 2/3 of its height, tapering gently into the rounded apex which is free from the column for ± 1/6 of its length

Morphology Reproductive morphology Flowers Androecium Stamens Anthers

Anther appendages fimbriate apically; anther wings linear, with ± parallel margins narrowing slightly from apex to base, drying white

Morphology Reproductive morphology Flowers Gynoecium Style

Stylar head appendage exserted for ± 1 mm from the column, clavate.

Morphology Reproductive morphology Fruits

Follicles and seeds not seen.

Ecology

Coastal forest and thicket on sand; 800 m

Distribution

Range: Only known from the type Flora districts: T8

Harris, T., & Goyder, D. (2007). A New Species of Secamone (Apocynaceae: Secamonoideae) from Southern Tanzania and a Re-Evaluation of S. Whytei. Kew Bulletin, 62(2), 281-284. Retrieved from http://www.jstor.org/stable/20443352

Type

Tanzania: T8. Lindi Distr.: Rondo Plateau, Rondo Forest Reserve, 6 km N of Forest Station, 10°04'S 39°13'E, 12 Feb. 1991, S. Bidgood, R. Abdallah & K Vollesen 1518 (holotypus K!; isotypus NHT).

Morphology General Habit

Slender woody twiner with white latex; young shoots pubescent with spreading reddish hairs; older stems glabrous

Morphology Leaves

Leaves very shortly petiolate, the petiole 0.2 - 0.4 mm long, densely reddish-pubescent; lamina 0.7 - 1.8 x 0.2 - 0.6 cm, narrowly ovate to elliptic, rarely linear or ovate, apex apiculate, base rounded, lower epidermis sparsely pubescent, the surface ± smooth, the stomata not obscured by minute papillae, upper epidermis smooth and glabrous; red hairs restricted to upper and lower midrib, principal veins mostly at c. 450 to the midrib

Morphology Reproductive morphology Inflorescences

Cymes mostly terminal, single-flowered, peduncle 0 1 mm long, glabrous

Morphology Reproductive morphology Inflorescences Bracts

Bracts 0.3 - 0.5 x 0.15 - 0.2 mm, linear or ovate and convex, apex acute or rounded with brown hairs at the margin

Morphology Reproductive morphology Flowers Pedicel

Pedicels 2 - 3.5 mm long, glabrous

Morphology Reproductive morphology Flowers Calyx

Calyx lobes 1 x 0.6 mm, ovate to broadly ovate, apex rounded, margins ciliate

Morphology Reproductive morphology Flowers Corolla

Corolla 3 - 4 mm long, yellowish-green; tube 0.5 - 1 mm long, corolla lobes 1.9 - 3 mm long, ovate oblong, apex rounded

Morphology Reproductive morphology Flowers Corona

Staminal corona lobes c. 0.5 x 0.1 - 0.2 mm, somewhat fleshy, adnate to the column from its base to 2/3 of its height, tapering gently into the rounded apex which is free from the column for c. 1/6 of its length Corolline corona of 5 fleshy ridges from the base of the corolla tube, dividing into pairs around the corolla lobe sinuses

Morphology Reproductive morphology Flowers Androecium Stamens Anthers

Anthers with small apical fimbriate appendages; anther wings linear, not reaching the top or bottom of the column, with ± parallel margins narrowing slightly from apex to base, drying white

Morphology Reproductive morphology Flowers Gynoecium Style

Apical portion of stylar head exserted for c. 1 mm from the column, clavate.

Distribution

Only known from a single collection from the Rondo Plateau in SE Tanzania. Potentially on the less collected Makondi Plateau and comparable plateaux in northern Mozambique.

Ecology

Bidgood et al. 1518 described the habitat as coastal forest and thicket regenerating after cultivation, on sand; alt. c. 800 m. Vollesen (1980: 8), in an outline of vegetation types in the Selous Game Reserve just north of the Rondo Plateau, refers to these coastal forests as completely deciduous, standing on deep sandy soils and occurring only above an altitude of 400 m.

Conservation

The species is known from fewer than five locations and is thus provisionally assessed as Vulnerable (VU D2) under Criterion D of IUCN (2001), though this may be downgraded to Near Threatened or Least Concern if further populations are discovered in this under-collected region. According to Vollesen (pers. comm.) much of the natural forest of the Rondo Plateau was felled for timber in the 1950s. Some areas were replanted with native and introduced timber species while other areas have regrown into a type of secondary forest that resembles the natural forest to varying degrees. Such habitat conversion may have affected the area of habitat suitable for Secamone clavistyla.

Note

Secamone clavistyla was compared most closely with S. delagoensis Schltr. due to similarity particularly in overall corolla size. Secondly, differences noted following comparison of S. clavistyla with both S. punctulata Decne. and S. filiformis (L. f.) J. H. Ross are detailed. Secamone clavistyla has a shorter corolla tube than S. delagoensis (c. 0.5 mm vs. 1.2 - 1.8 mm) and a shorter peduncle (c. 0.5 mm vs. 2 - 4 mm) giving it a subsessile rather than clearly pedunculate inflorescence. The flowers of the new species are solitary, whereas S. delagoensis can have up to four flowers in an inflorescence. S. delagoensis is completely glabrous whereas S. clavistyla has spreading reddish hairs on younger shoots, the petiole and the midrib on both upper and lower leaf surfaces. Comparisons highlighted not only differences in morphological characters, but also substantial differences in distribution and habitat. Secamone delagoensis is completely restricted to the sand forests of the Maputaland centre of endemism in the extreme south of Mozambique and the most northerly parts of KwaZulu-Natal (Van Wyk 1994, 1996; Van Wyk & Smith 2001). This region is some 2000 km south of the Rondo Plateau, where S. clavistyla was collected at an altitude of 800 m. The S. delagoensis collections seen came from an altitude of 30 -80 m. While Secarmone filiformis has a corolla tube of similar size to S. clavistyla, the new species differs from both S. filiformis and S. punctulata in its reduced, unbranched rather than branched inflorescence, its larger corolla (3 - 4 mm vs. 1.5 - 2(- 3) mm), and its larger, more exserted stylar head (c. 1 mm vs. 0 - 0.4 mm).