Croton mayottae P.E. Berry & Kainul., 2017

Kainulainen, Kent, Ee, Benjamin van, Razafindraibe, Hanta & Berry, Paul E., 2017, A revision of the Adenophorus Group and other glandular-leaved species of Croton (Euphorbiaceae) from northern Madagascar and Mayotte, including three new species, Candollea 72 (2), pp. 371-402 : 392-394

Croton mayottae P.E. Berry & Kainul. , spec. nova ( Fig. 2E , 9 ).

Typus: FRANCE. Dept. Mayotte: Grande-Terre, Chiconi , village , 16.I.2001, Barthelat, M’Changama & Sifary 225 (holo-: P [ P00229211 ]!; iso-: G [ G00341697 ]!, K!, MAO, MO!).

= Croton regeneratrix var. mayottensis Radcl.-Sm. , Gen. Croton Madag. Comoro 202. 2016. Typus: FRANCE. Dept. Mayotte: Rassi Maoussi , 30 m, 24.IV.1997, Pascal 915 (holo-: K!; iso-: BR, G [ G00341698 ]!, MO!, P [ P00144592] !, WAG), syn. nov.

Croton mayottae P.E. Berry & Kainul. is similar to C. loucoubensis Baill. but differs in its cordate (vs rounded) leaf bases, serrulate stipules (vs fimbriate), stellate-pubescent (vs bristly hirsute) ovary, and smaller and thinner-walled capsules (c. 7 mm diam. with endocarp c. 0.4 mm thick vs ≥ 10 mm diam. with endocarp c. 2 mm thick).

Shrubs 2-3 m tall, dichotomously branching. Branches terete, with a scurfy indument of short, tan-colored, fasciculatestellate trichomes. Older stems smooth, matte tan to pale gray, glabrescent, with lighter-colored oval lenticels, with reddish latex. Stipules 10-20 mm long, narrowly lanceolate, finely serrate along the margins, with an aristate tip, caducous. Leaves opposite, apparently deciduous; leaf scars conspicuous and drying much darker than the adjacent stem tissue. Petioles 1.5-6 cm long, densely scurfy-pubescent like the young stems, with a pair of subsessile, concave, discoid glands (0.4-0.6 mm diam.) on the lower side of the base of the lamina. Leaf blades firmly papyraceous, finely denticulate, ovate, 5-10 × 3-6 cm, apex acuminate, base cordate; both sides covered with a moderately dense cover of stellate trichomes (these not overlapping, so leaf surface can be seen underneath), green when fresh and drying matte pale green; venation 5- or 7-palmate at the base, with 2-6 pairs of penninerved secondary veins from around the middle of the blade, veins prominent and lighter-colored on abaxial side, usually with some acetabuliform glands in the axils of some of the secondary and tertiary veins ( Fig. 9B ). Inflorescences terminal, raceme-like thyrses, 6-10 cm long, with c. 4-12 pistillate flowers in the basal part and numerous staminate flowers distally, axes densely tan-scurfy with tightly fasciculate trichomes; bracts triangular, 2-4 × 1-2 mm, semipersistent. Staminate flowers with densely scurfy, subglobose buds 1.5- 2.5 mm diam., pedicels 2-7 mm long; sepals 5, shortly connate at base, lobes broadly triangular-ovate, 2-2.5 × 2.2-3 mm, apex acute, inflexed at anthesis, abaxially stellate-pubescent, adaxially stellate towards apex, margins ciliate; petals 5, elliptic to spatulate, 2-2.8 × 1-1.7 mm, recurved at anthesis, abaxially stellate and papillose, adaxially glabrous, margins densely ciliate; disc glands 5, opposite the sepals, sessile, ellipsoidal with an apical depression, c. 0.5 × 0.5 mm, yellow; stamens c. 14, white, filaments 2-3 mm long, glabrous, anthers broadly elliptic, c. 1 × 0.9 mm; receptacle pilose. Pistillate flowers with densely scurfy-stellate buds 2-2.5 mm diam., pedicels 3-6 mm long; sepals 5, triangular, 2-3.5 × 1.5-2.5 mm, apex acute, densely tan-scurfy abaxially and adaxially stellate, petals absent or reduced to short filaments ca 1.5 mm long; disc glands 5, opposite the sepals, sessile, ellipsoidal, c. 0.4 × 0.8 mm, yellow; ovary globoid, 2.7-4 mm diam., densely covered by compact, golden-stellate trichomes; styles 3, 1.5-3.3 mm long, each branch flattened and twice bifurcate, spreading, abaxially stellate-pubescent, adaxially glabrous, persistent. Capsules c. 6 mm long, light brown, puberulent, the endocarp woody, c. 0.4 mm thick; columella 4.5-5 mm long, the apex cornute with partially recurved fibers. Seeds broadly compressed-ellipsoid, c. 4.7 × 3.8 × 2.7 mm; testa matte, light brown, slightly rugulose; caruncle shield-shaped, c. 1 × 1.5 mm.

Etymology. – Named after the island of Mayotte, in the Comoros Archipelago, where this species is endemic.

Phenology. – Specimens in bud have been collected in March and April, flowering specimens in October–November and in January, and a specimen in fruit in November.

Distribution, habitat and ecology. – Croton mayottae occurs in seasonally dry forest, mainly near the coastline, on the Grande-Terre island of Mayotte at elevations from sea level to 170 m ( Fig. 2E ).

Conservation assessment. – Since the species in endemic to the island of Mayotte and restricted there to coastal forest remnants in only four localities, we consider it to be “Endangered” [EN B1ab(iii)] according to IUCN Red List Categories and Criteria ( IUCN, 2012).

Vernacular names. – “M’Houvé” (Soumille 992), “Mouhouve” (Hoffman & Ranmanana 363), “Muhuve [in Shibushi, Shimahorais]” (Barthelat & Rolland 1324), “Sary lazalaza” (Barthelat & Rolland 1324).

Notes. – RADCLIFFE-SMITH (2016) based his description of C. regeneratrix var. mayottensis on a single collection in early bud, and he failed to note that it had opposite leaves and glands on the undersides of the leaves, whereas C. regeneratrix has alternate leaves that lack laminar glands. He treated another specimen of C. mayottae (Pascal 724) as C. adenophorus . Rather than making a combination based on the type of Radclife-Smith’s variety, we prefer our choice of type for C. mayottae , which has open pistillate and staminate flowers and is much more diagnostic for the species. The other native Croton species on Mayotte include C. humblotii Baill. , which also occurs on the three islands of the Union of the Comoros; C. bifurcatus Baill. , and C. emeliae Baill. , which like C. mayottae are found only on Mayotte; and finally C. adenophorus , which occurs mainly on mainland Madagascar in Antsiranana Province.

Additional specimens examined. – FRANCE. Dept. Mayotte: Saziley , 21.III.2004, Barthelat & Rolland 1324 ( G, K, MAO, MO, P); Combani , Parcelle de Bakar , 11.IV.2001, Hladik 6534 ( P); Saziley, 12.IV.2001, Hladik 6558 ( P); ibid loc., 12°58’S 45°11’E, 170 m, 11.XI.2002, Hoffman & Ralimanana 363 ( G, K, MAO, MO, P, TAN); ibid loc., 80 m, 17.X.1996, Pascal 724 ( MO, P); Sazilé Bé , 12°58’39”S 45°12’01”E, 100- 150 m, 11.IV.1999, Pignal 1111 ( G, K, P); Saziley , 0 m, 14.XI.1997, Soumille 992 ( G, K, MO, P, WAG) .

Figures

Fig. 2. Distribution maps. A. Croton nudatus Baill. (white), C. stanneus Baill. (yellow); B. Croton adenophorus Baill. (green) and C. tsiampiensis Leandri (white); C. Croton bathianus Leandri (light blue), C. loucoubensis Baill. (yellow), and Croton scoriarum Leandri (red); D. Croton orangeae Kainul. & Berry (red) and C. sahafariensis Kainul. & Berry (yellow); E. Croton mayottae P.E. Berry & Kainul. [Google Earth Image © 2017 DigitalGlobe. Reproduced per attribution guidelines]

Fig. 9. Croton mayottae Berry & Kainul. A. Flowering branch with staminate flowers; B. Abaxial side of leaves showing laminar glands and pubescence; C. Staminate flower; D-F. Pistillate flower; F. Top-view with the ovary removed to show the five nectaries.