Croton radiatus P.E. Berry & Kainul., 2016

Kainulainen, Kent, Ee, Benjamin van, Antilahimena, Patrice, Razafindraibe, Hanta & Berry, Paul E., 2016, New species and species reports of Croton L. (Euphorbiaceae) from the eastern forest corridor of Madagascar, Candollea 71 (2), pp. 327-356 : 339-340

Croton radiatus P.E. Berry & Kainul. , spec. nova ( Fig. 1C , 11 ).

Typus: MADAGASCAR. Prov. Toamasina: Alaotra- Mangoro Region, Moramanga Distr., Commune Ambohibary, Fokontany Ampitambe , Forêt Sahaevo , 18°49’59”S 48°17’47”E, 1118 m, 11.XII.2006, Razanatsoa & Marcellin 279 (holo-: MICH [ MICH1458525 ]!; iso-: MO!, TAN!).

Croton radiatus P.E. Berry & Kainul. is similar to Croton incisus Baill. , but differs in its leaves that are entire to shallowly serrulate or undulate (vs incised), and in the foliaceous, glabrous sepals (vs. densely stellate-pubescent). In its tightly clustered, medium-sized leaves that are separated by long internodes it resembles Croton hypochalibaeus Baill. , but differs in its sparser pubescence with scattered stellate trichomes on the leaves (vs. densely silvery white-lepidote and brown punctulate leaves).

Shrubs to 0.8-2 m tall, dichotomously or trichotomously branching, with elongate internodes 2-7 cm long separating clusters of opposite or ternate leaves at the nodes, giving the appearance of whorled branches. Branches terete, pale gray, the young growth densely covered by scurfy, brownish, fasciculate to multiradiate trichomes, the longest rays 1.5-2.5 mm long, the other rays 1.5-2 mm long, interspersed with smaller, whitish stellate-lepidote trichomes with a porrect, brownish central radius 1-1.5 mm long. Stipules absent or 1-1.5 mm long and subulate. Leaves congested and ± whorled at apex and at nodes. Petioles 1-5 mm long, pubescent like the stems. Leaf blades papyraceous, entire, serrulate, or with shallow irregular undulations, elliptic, 15-50 × 7-20 mm, apex and base acute; adaxial surface medium green and subglabrous, abaxial surface much paler olive-green, mostly glabrous but with widely scattered fasciculate and stellate trichomes, especially along the nerves; venation faint, with 5-7 pairs of brochidodromus, ± penninerved secondary veins; basilaminar glands present in some leaves (but absent in over half of them), when present emerging from the abaxial side several mm from the base of the blade, usually in pairs, sometimes single, stipitate (1.0- 2.5 mm), discoid (1.0- 1.8 mm diam.), concave. Inflorescences racemose, 8-12 mm long, axillary at leafy nodes, axis pubescent like the stems, usually with two basal pistillate flowers and 5-10 distal staminate flowers, bracts lanceolate, pale, c. 1 mm long. Staminate flowers with subglobose buds 0.8- 1.7 mm diam., pedicels 2.5-4 mm long; sepals 5, lobes broadly triangular to ovate, c. 1.4 × 1.2. mm, apex acute to rounded, abaxially with scattered whitish stellate-lepidote trichomes with a porrect brownish radius, adaxially glabrous, white; petals 5, white, spatulate, c. 1.5 × 0.5 mm, abaxially papillate, adaxially glabrous, margins densely ciliate; disc glands/ nectaries 5, opposite the sepals, sessile, broadly triangular and truncate, c. 0.4 × 0.4 mm, yellowish; stamens 8-12, white to pale yellow, filaments c. 2.0 mm long, ciliate, anthers elliptic, c. 0.6 mm long; receptacle pilose. Pistillate flowers with pubescent pedicels 2-7 mm long; sepals 5, light green, ± foliaceous with longitudinal veins evident, oblong to spatulate, somewhat unequal, apex acute to rounded, spreading at anthesis, 2-5 × 1.5-2 mm, abaxially with a few scattered stellate trichomes, adaxially glabrous; disc glands/nectaries 5, opposite the sepals, sessile, rounded, c. 0.5 × 0.4 mm, pale yellow; glandular filaments 5 (in petal position alternating with sepals), c. 0.9 mm long; ovary globose, 1.5-2.0 mm diam., densely stellate, styles 3, 10- 16 mm long, terete, ascending, each bifurcating twice (yielding 4 stigmatic tips per branch, or c. 12 overall), abaxially with a few scattered stellate trichomes; ovary densely hirsute, with stiff, light brown fasciculate trichomes with radii 1.2- 1.5 mm long. Capsules and seeds not seen.

Etymology. – The specific epithet refers to the radiate nature of the prominent trichomes, which are rather sparsely scattered on the abaxial leaf surface but much denser along the young shoots.

Phenology. – Of the four known specimens, one was collected in flower in December and the others in April and late July, which indicates the species is probably aseasonal in its flowering.

Distribution, habitat and ecology. – Croton radiatus is known so far from four collections, in dense, humid, montane forests along the eastern escarpment of Madagascar in the Ankeniheny-Zahamena forest corridor in the Alaotra-Mangoro and Analanjirofo Regions of Toamasina Prov., at elevations of 900-1120 m ( Fig. 1C ).

Notes. – Croton radiatus shows a similar sylleptic growth pattern to other species like C. hypochalibaeus , in which long internodes separate nodes where the leaves are clustered ( Fig. 11A , 13A ). This may just represent growth spurts stimulated by periodic periods of rains following warmer, dry periods. The new species is distinctive in the ± foliaceous sepals of the pistillate flowers along with the stiffly hirsute ovary.

According to the classification of foliar trichomes in WEBSTER et al. (1996), the larger brownish trichomes of C. radiatus are fasciculate or multiradiate, with the radii ascending rather than in one plane, and they vary from up to 8 radii per trichome (fasciculate) to more than 8 per trichome (radiate). The smaller, interspersed, whitish trichomes are stellate-lepidote with a larger, porrect, and brown central radius (see Fig. 11 C-D). Similar, but much shorter trichomes are also characteristic of C. ankeranae and C. indrisilvae .

Paratypi. – MADAGASCAR. Prov. Toamasina: Alaotra-Mangoro Region, Ambatondrazaka Distr., env. du Lac Alaotra (S-39) , IV.1939, Cours 1257 ( P); chutes du Maningory , Lac Alaotra (S -39) , s.d., Herb. Jard. Bot.Tan. 3769 ( P); Analanjirofo Region, Vavatenina Distr., Ambodimangavalo , Antevibe , Sahandrazana à 3 km au NW d’Antevibe, hors du Parc National de Zahamena, 17°32’S 48°48’E, 900 m, 31.VII.2003, Rakotondrajaona et al. 298 ( CNARP, MICH, MO, P, TEF).

Figures

Fig. 1. – Distribution maps. The grey squares or white arrow on the inset maps of Madagascar show the location of the area depicted. A. Croton ferricretus Kainul., B.W. van Ee & P.E. Berry (red); B. Distribution of Croton droguetioides Kainul. & Radcl.-Sm. (turquoise) (Cours 4111 not shown), C. enigmaticus P.E. Berry & B.W. van Ee (light green) (Ralimanana et al. 1402 not shown), C. indrisilvae Kainul., B.W. van Ee & P.E. Berry (yellow), and C. plurispicatus P.E. Berry, Kainul. & B.W. van Ee (light purple); C. Croton ankeranae Kainul. (yellow), C. radiatus P.E. Berry & Kainul. (red), and Croton lasiopyrus Baill. (white). The collection in gray represents presumed hybrids between C. lasiopyrus and C. enigmaticus (van Ee et al. 2215 and 2216); D. Croton hypochalibaeus Baill. in Madagascar. [Google Earth Image © 2016 DigitalGlobe.Reproduced per attribution guidelines]

Fig. 11. – Croton radiatus P.E. Berry & Kainul. A. Holotype specimen of Croton radiatus at MICH; B. Inflorescence with a pair of basal pistillate flowers and five distal staminate flower buds; C. Underside of a leaf showing both whitish stellate-lepidote trichomes and brown fasciculate to multiradiate trichomes; D. Leaf base with a pair of stipitate, discoid glands emerging from the lamina; E. Staminate flower (7 anthers missing); F. Staminate flower with stamens removed to show the nectaries; G. Pistillate flower; H. Top view with the ovary removed to show the five nectaries and glandular filaments. [E-F: Cours 1257; G-H: Razanatsoa & Marcellin 279]

Fig. 13. – Croton hypochalibaeus Baill. A. Habit; B. Stem (diam. c. 2.5 cm) with cauliflorous flowers; C. Close-up of the underside of a leaf; D. Staminate flower; E-F. Pistillate flowers; G-H. Fruits. [Photos: P. Berry]