Croton scoriarum Leandri in Adansonia, sér. 2, 12: 68. 1972

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 : 398-399

Croton scoriarum Leandri in Adansonia, sér. 2, 12: 68. 1972 . ( Fig. 1H , 2C , 12 ).

Lectotypus (designated here): MADAGASCAR. Prov. Mahajanga: Centre, au lieu dit Analankeboka , à l’W de Bealanana , 20.XI.1966, Service Forestier 27107 ( P [ P00706283 ]!; isolecto-: K [ K000895678 ]!, P [P00706284]!, TEF [ TEF000183 ]!) .

= Croton bathianus var. ambatondrazakae Radcl.-Sm., Gen. Croton Madag. Comoro 114. 2016 . Typus: MADAGASCAR. Prov. Toamasina: Alaotra-Mangoro Reg. , Ambatondrazaka Distr ., Menaloha , 900 m, XI.1937, Cours 587 (holo-: P [ P00127483 ]!), syn. nov.

Shrubs or trees 1.5-8 m tall, dichotomously branching. Branches flattened on new growth but becoming terete with age, initially green with a farinose cover of whitish, stellate trichomes, but soon turning reddish-brown and glabrous. Mature bark papery and flaky. Stipules 2-7 × 1-1.5 mm, lanceolate, with marginal glands, early caducous. Leaves opposite, deciduous. Petioles 1-10 cm long, adaxially canaliculate, stellate-pubescent at first, soon glabrous, usually with a pair of acropetiolar, ± stipitate glands with a concave, discoid, yellow apex (0.5-1 mm diam.). Leaf blades chartaceous, ± entire, ovate, 4.5-22 × 3-15.5 cm, apex acuminate, base rounded to cordate; young leaves with a dense, farinose cover of whitish, stellate trichomes with brownish trichomes also present along the abaxial veins, both sides soon becoming glabrous, pale green when fresh and drying matte yellowish green to dark green-brown; venation prominent, with 6-9 pairs of brochidodromus, ± penninerved secondary veins (the lowermost pairs congested and appearing palmate), and cross-venulate tertiary venation; with ± stipitate glands in some of the axils of the secondary veins ( Fig. 1H ). Inflorescences terminal, raceme-like thyrses 2-11 cm long, with pistillate flowers on the lower and middle part of the axis and staminate flowers towards the distal end, axes stellate-pubescent, flattened; bracts triangular, c. 2.5 mm long, caducous. Staminate flowers with stellate, subglobose buds 1.8-2 mm in diam., pedicels 1-4 mm long; sepals 5, shortly connate at base, lobes ovate, c. 2 × 1.8 mm, apex acute, inflexed at anthesis, abaxially stellate, adaxially sparsely ciliate, margins ciliate; petals 5, white, elliptic-obovate, 2.5-3 × 1-1.3 mm, recurved at anthesis, abaxially stellate and papillose, adaxially glabrous, margins ciliate; disc glands 5, opposite the sepals, sessile, ellipsoidal with an apical depression, c. 0.5 × 0.8 mm, yellowish; stamens 15-20, white, filaments 2-3 mm long, pilose at base, anthers broadly elliptic, c. 0.8-1 × 0.7- 0.9 mm; receptacle pilose. Pistillate flowers with stellate ellipsoid buds, c. 1.8 mm diam., pedicels 1-3 mm long; sepals 5, ovate, spreading at anthesis, c. 2.5 × 1.3-2.0 mm, pale green, apex acute, shortly connate at base, abaxially stellate, adaxially sparsely pubescent, petals often reduced, if present similar to the petals of the staminate flower; disc glands 5, opposite the sepals, sessile, ellipsoidal, c. 0.5 × 0.3-1.3 mm; ovary stellate, globoid, c. 2.5 mm diam; styles 3, 2- 3 mm long, each branch flattened and twice bifurcate, spreading, abaxially stellate, adaxially glabrous, yellow, turning brown, persistent. Capsules and seeds not seen.

Phenology. – This species has only been collected from September to March, presumably because it is deciduous during the dry season. Specimens in flower have been collected from September to December, with immature fruits in October.

Distribution, habitat and ecology. – This species has a disjunct distribution and has been collected in deciduous forests in western Antsiranana Province (Ambilobe, Ankarana National Park, and Sakaramy), northern Mahajanga (Ambodimotso and Bealanana), and in the Lac Alaotra area in Toamasina Province, growing on basalt, lateritic and sandy soils at 100-900 m in elevation ( Fig. 2C ).

Conservation assessment. – Croton scoriarum has been collected only rarely from rather scattered localities, but may be extant in a wide area in central to northern Madagascar. With probably more than ten locations in three Provinces, we assigned this species as “Least Concern” [LC] according the IUCN Red List Categories and Criteria ( IUCN, 2012).

Vernacular names. – “Hazompondra” (Herb. Jard. Bot. Tana 5252).

Notes. –The species epithet scoriarum refers to the volcanic substrate on which the type was collected.

The species can be distinguished from its congeners by its large mature leaves that are ovate with a rounded-truncate base and entire to shallowly undulate or denticulate margins. The leaves are densely whitish stellate-pubescent on both sides when young but then become almost completely glabrous with age ( Fig. 1H , 12 C-D). The shoots likewise become smooth, and usually dry a glossy dark reddish-brown. The mature bark is papery and thinly flaky. In the molecular phylogenetic study of Malagasy Croton by HABER et al. (2017), C. scoriarum was called “ Croton sp. nov. K”, and it formed a clade with C. adenophorus and C. bathianus (therein called “ C. cf. loucoubensis ”); all three accessions share an asparagine-arginine insert in maturase K. In his protologue, LEANDRI (1972), mentioned the specimen Service Forestier 26207 (P) from the Antsalova District of Mahajanga Province as possibly belonging to C. scoriarum . We think that this specimen may be better included in C. crocodilorum Leandri , or else treated as a separate species. Croton crocodilorum is similar to C. scoriarum but has smaller leaves with a cordate base and denticulate margin, and it appears to retain a dense stellate indument, at least on the abaxial side of the leaves. The specimens from the Lac Alaotra surroundings, some of which have been recognized as C. bathianus var. ambatondrazakae Radcl. -Sm., all appear to have been collected at the onset of the rainy season (November) and have no leaves, or else very small leaves. This makes it difficult to confidently determine them to species, but the thinly flaky, glossy, and dark brown bark is consistent with their placement in C. scoriarum , although further collections may prove them to be a distinct species.

Additional specimens examined. – MADAGASCAR. Prov. Antsiranana: Diana Reg. , Ambilobe , 26.VII.1939, Decary 14584 ( P); Two-track road from Sakaramy towards Mahatsinja , west of road from RN 6 to Joffreville , 12°25’59”S 49°16’19”E, 340 m, 27.X.2009, van Ee et al. 1118 ( MICH); ibid loc., van Ee et al. 1120 ( MICH); ibid loc., van Ee et al. 1129 ( MICH); ibid loc., 12°24’33”S 49°17’05”E, 321 m, 3.III.2016, van Ee et al. 2329 ( MICH, TAN); Ankarana National Park , 12°56’52”S 49°07’33”E, 118 m, 7.III.2016, van Ee et al. 2379 ( MICH, TAN). Prov. Mahajanga: Sofia Reg ., Ambodimotso , bas-Befandriana Nord , 14.IX.1942, Herb. Jard. Bot.Tana 5252 ( P). Prov. Toamasina: Alaotra-Mangoro Reg ., Antsihanaka , XI.1936, Herb. Jard. Bot. 2202 ( P); ibid loc., XI.1936, Herb. Jard. Bot. 2287 ( P); Lac Alaotra ( G), s.d., Herb. Jard. Bot. 3959 ( P) .

Figures

Fig. 1. Abaxial side of leaves showing laminar glands and pubescence A. Croton nudatus Baill.; B. Croton stanneus Baill.; C. Croton adenophorus Baill.; D. Croton bathianus Leandri; E. Croton loucoubensis Baill.; F. Croton orangeae Kainul. & Berry; G. Croton sahafariensis Kainul. & Berry; H. Croton scoriarum Leandri; I. Croton tsiampiensis Leandri. [A: van Ee et al. 2340; B: van Ee et al. 2160; C: van Ee et al. 1135; D: van Ee et al. 1138; E: Ammann et al. 378; F: van Ee et al. 2353; G: van Ee et al. 1089; H: van Ee et al. 2329; I: Nusbaumer LN 902]

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. 12. Croton scoriarum Leandri A. Habit; B. Bark; C. Mature leaves; D. Underside of young leaf; E. Inflorescence with staminate flowers and buds; F-G. Inflorescences with pistillate flowers; H. Young fruits. [A, C, D: van Ee et al. 2329; B, E-F: van Ee et al. 1118; G-H: van Ee et al. 1129] [Photos: A, C: K. Kainulainen; B, D-H: P. Berry]