Croton vatomandrensis Leandri

Kainulainen, Kent, Berry, Paul E. & Ee, Benjamin van, 2017, Rediscovery of two species of Croton (Euphorbiaceae) from littoral habitats of eastern Madagascar, Candollea 72 (1), pp. 35-44 : 39-44

Croton vatomandrensis Leandri in Ann. Mus. Colon. Marseille, sér. 5, 7: 71. 1939 ( Fig. 1 , 3 , 4 G-L, 5C-D).

Lectotypus (designated here): M ADAGASCAR. Prov.Toamasina: env. de Vatomandry, près des lagunes, XI.1921, Perrier de la Bâthie 14084 ( P [ P00248926 ]!; isolecto-: P [ P 00154409, P 00154410]!).

Shrubs or small trees 1-3(-7) m tall, sparsely branched with dichotomous branching, stems ascending and semi-succulent, often with distinct horizontal or reticulate furrows in the bark, internodes sometimes contracted, giving the appearance of whorled branches. Branches ± flattened on new growth but becoming terete with age, gray, densely covered with redbrown stellate-lepidote indumentum that soon turns pale gray. Stipules absent or vestigial. Leaves alternate along stem, but (sub)opposite towards the apex. Petioles 2-15 mm long, adaxially canaliculate, densely red-brown stellate-lepidote, usually with a pair of concave discoid glands c. 1 mm in diam. near the base of the blade. Leaf blades coriaceous, entire or very shallowly serrulate towards the apex, elliptic to obovate, 3-16 × 1.8-3 cm, apex acute, obtuse, or rounded, base cuneate; adaxial surface ± glabrous, glossy, bright green when fresh, turning orange in old leaves, drying matte pale green; venation not prominent, with 5-10(-16) pairs of brochidodromus, ± penninerved secondary veins; abaxial surface sparsely brown stellate-lepidote, pale green and glossy; venation not prominent except for the midrib. Inflorescences spike-like or pseudoracemose cymes, 5-15 cm long, terminal, erect, bisexual, the staminate flowers towards the distal end and more numerous than the pistillate flowers at the base; axes densely stellate-lepidote, flattened; bracts narrowly triangular, 0.9-1.6 mm long. Staminate flowers with brown stellate-lepidote, subglobose buds 1.6-2.6 mm diam., pedicels elongating from bud to anthesis, to 4 mm long; sepals 5, pale green, shortly connate at base, lobes broadly triangular-ovate, 1.2-1.8 × 1.0- 1.6 mm, apex acute, inflexed at anthesis, abaxially sparsely stellate-lepidote and papillose, adaxially glabrous, margins ciliate; petals 5, white, elliptic-spatulate, c. 2 × 1 mm, recurved at anthesis, abaxially papillate and pilose towards base, adaxially glabrous, margins densely ciliate; disc glands/nectaries 5, opposite the sepals, sessile, ellipsoidal with an apical depression, c. 0.6 × 0.3 mm, yellow; stamens 13-16, white, filaments 1.3-2.5 mm long, ciliate, anthers elliptic, c. 0.6 × 0.5 mm; receptacle pilose. Pistillate flowers with stellate-lepidote buds 1.8-2.8 mm diam., pedicels to 4 mm long; sepals 5, firm, elliptic, not spreading at anthesis, 2.2-3.5 × 1.1- 1.6 mm, apex acute, shortly connate at base, abaxially brown stellate-lepidote, adaxially glabrous, pale green, persistent in fruit; petals absent/reduced; disc glands/nectaries 5, opposite the sepals, sessile, ellipsoidal, c. 0.6 × 0.3 mm, pale yellow; glandular filaments alternating with the sepals, 0.8-1.5 mm long; ovary glabrous, green, globoid-ellipsoid, c. 2.5 mm diam., styles 3, 3.0– 3.5 mm long, each branch flattened and twice (or thrice) bifurcate for a total of 12 stigmatic tips, spreading, recurved at the apices, abaxially and adaxially glabrous, white, turning brown, persistent. Capsules 4.5-5.0 × 4.5- 6.8 mm, smooth, green to brown, glabrous, exocarp not separating, endocarp woody, c. 0.2 mm thick; columella c. 4.5 mm long, cornute, capitate. Seeds ± compressed-ellipsoid, c. 4.6 × 3.3 mm; testa glossy, granulate, dark brown; caruncle narrowly reniform, c. 0.6 × 0.2 mm.

on sand at Sainte Luce, Anosy Region, Toliara Province; C. Branch with leaves; note the villous pubescence on this specimen from Sainte Luce; D. Branch with staminate flowers and immature fruits; E. Staminate flowers; F-G. Pistillate flowers; H. Mature fruit.

[C: van Ee et al. 2148; D: van Ee et al. 927; E-G: van Ee et al. 2138; H: van Ee et al. 926] [Photos: P. Berry]

Distribution, habitat, and ecology. – Croton vatomandrensis is known from three sites so far, two in Toamasina Province and one in Fianarantsoa Province, all in sandy, swampy, littoral habitats, from sea level to around 30 m elevation. The type collection from Vatomandry was collected at the edge of a lagoon, and the specimens from Mahabo are from moist, somewhat boggy areas within the littoral forest and grassland zone, where they were growing mostly at the edge of patches of shrubs or Ravenala in areas with standing water, Sphagnum , ferns, grasses, and sedges ( Fig. 1 , 3 A-B).

Phenology. – Based on the few known collections, Croton vatomandrensis appears to flower and fruit most heavily towards the end of the calendar year (November). In July at Mahabo we found plants mostly in the young bud stage, and the collection from Vohibola in Toamasina Province was fruiting in August.

Conservation status. – Besides the type locality near Vatomandry in southeastern Toamasina Province, Croton vatomandrensis is presently known from the forest of Vohibola farther north in Toamasina, and a small area near Mahabo, in Fianarantsoa Province. No collections have been made of it from the type locality near Vatomandry since the type was collected in 1921. Whereas C. chapelieri was locally common in the sandy forests at Mahabo, we saw very few individuals of C. vatomandrensis there. Given the restricted occurrences in just three known localities and the threat of habitat destruction in those sites, we recommend that this species be assessed as “Endangered” [EN B2ab(ii, iii, iv)], following the IUCN Red List Categories and Criteria (IUCN, 2012).

Notes. – Croton vatomandrensis is distinct with its sparsely branched habit and slightly succulent stems, the glabrous leaves and fruits, and the stellate-lepidote indumentum on young shoots that is reddish brown when young but turns pale gray with age ( Fig. 3D ). The erect spike-like inflorescences are also characteristic ( Fig. 3G ). It is notable that they appear to be dormant for extended periods of time before the onset of flowering. When Leandri (1939) described this species, he placed it in the informal “Groupe Fothergillifolium” together with C. fothergillifolius from Mauritius and C. furcellatus Baill. from Madagascar. Although he included all three species in his key to the group, there was no corresponding species entry for C. furcellatus . Instead, he included that species at the end of the article in his list of insufficiently known or doubtful species, mentioning that it might represent an introduction or a mislabeling. Although the type label of C. furcellatus indicates it is a Scott-Elliot collection from Fort Dauphin in southeastern Madagascar, it was actually mislabeled at Paris in a shipment that had been received from Kew (an error documented by Humbert, 1948). The type specimen of C. furcellatus is in reality a New World Croton , C. sonorae Torr. , most likely an Edward Palmer collection (Palmer 180) from northern Mexico.

Both Leandri’s “Groupe Fothergillifolium” and “Groupe Chapelieri” were characterized as having staminate flowers with more than 12 stamens, a lack of lepidote scales, two acropetiolar glands (with no other glands on the leaf surface), leaves glabrescent on the abaxial surface, and petals of the pistillate flowers rudimentary or lacking (Leandri, 1939). The only difference in Leandri’s key between the groups was one of leaf blade proportions (blade at least twice as long as wide in Groupe Chapelieri and blade at least half as wide as long in Groupe Fothergillifolium). In a recent molecular study of Western Indian Ocean species of Croton (Haber et al., in press), C. fothergillifolius is part of a highly supported clade of four species confined to the Mascarene island of Mauritius, whereas C. chapelieri and C. vatomandrensis are both embedded within a broader group of Malagasy, African, and Comoro Islands species, and they furthermore form part of the same, albeit poorly supported clade together with C. bracteatus and another undescribed species. This shows at least that C. vatomandrensis does not belong in the same group as C. fothergillifolius , and that the circumscription of Groupe Chapelieri needs to be examined in greater detail to determine whether C. vatomandrensis is actually closely allied to C. chapelieri or not.

B

1 mm

Additional specimens examined. – MADAGASCAR. Prov. Fianarantsoa: Atsimo-Atsinanana Region, Farafangana District , Mahabo-Mananivo, Baboaka, forêt Marovahatry , au bord du marécage Andranokena, 23°10’41”S 47°43’49”E, 23 m, 21.IV.2004, Ludovic 737 (MO); Mahabo, 23°11’09”S 47°42’22”E, 15 m, 9.XI.2001, McPherson & Rabenantoandro 18384 ( K, MO, P); ibid. loc., 23°10’13”S 47°43’27”E, 22 m, 26.VII.2003, Rabehevitra et al. 550 ( K, MO, P, TEF); ibid. loc., 23°10’20”S 47°42’23”E, 29 m, 23.IX.2002, Rabenantoandro et al. 957 ( K, MICH, MO); ibid. loc., 11.XI.2002, Razakamalala & Ludovic 329 ( K, MICH, MO); ibid. loc., 23°10’21”S 47°43’11”E, 0-50 m, 11.IX.2009, van Ee et al. 1194 ( MICH, TAN); ibid. loc., 23°10’16”S 47°41’58”E, c. 15 m, 19.VII.2015, van Ee et al. 2028 ( MICH, MO, P, TAN); ibid. loc., 23°10’19”S 47°41’48”E, 15 m, 19.VII.2015, van Ee et al. 2029 ( MICH, MO, P, TAN). Prov. Toamasina: Atsinanana Region, Brickaville Distr., Andranonkoditra, Ankanin’ny nofy, Vohibola forest , 18°33’56”S 49°15’24”E, 8 m, 4.VIII.2003, Rabehevitra et al. 405 ( K, MICH, MO).

Figures

Fig. 1. – Geographic distribution of Croton chapelieri Baill. (stars) and C. vatomandrensis Leandri (circles), mapped on the bioclimatic zones of Madagascar (after CORNET, 1974; see SCHATZ, 2000).

Fig. 3. – Croton vatomandrensis Leandri. A. Typical littoral habitat at Mahabo, Atsimo-Atsinanana Region, Fianarantsoa Province; B. Habit; C. Bark; note the characteristic horizontal furrows; D. Branch; note the subverticillate branching and how the young shoots soon turn from reddish brown to pale gray; E. Inflorescence with staminate flower and buds; F. Staminate flower; G. Immature inflorescences; H. Inflorescence with pistillate flowers; note the erect sepals; I. Pistillate flower and immature fruit; note the glabrous ovary. [A-C, G-H: van Ee et al. 2028; D-F, I: van Ee et al. 1194] [Photos: P. Berry]

Fig. 4. – Croton chapelieri Baill. (A-F) and C. vatomandrensis Leandri (G-L). A-C. Staminate flower: side view (A), top view (B) and top view with stamens removed to show the five nectaries (C). D-F. Pistillate flower: side view (D), top view (E), and top view with ovary removed to show the five nectaries (F). G-I. Staminate flower: side view (G), top view (H), and top view with stamens removed to show the five nectaries (I). J-L. Pistillate flower: side view (J), top view (K), and top view with ovary removed to show the five nectaries (L). [A-F: van Ee et al. 1181; G-L: van Ee et al. 1194]