Thilachium latifolium Fici, 2023

Fici, Silvio, 2023, A new species of Thilachium (Capparaceae) from the Analanjirofo Region, Madagascar, Bothalia (a 4) 53 (1), pp. 1-6 : 2-4

Thilachium latifolium Fici , sp. nov.

TYPE: MADAGASCAR, Analanjirofo Region, Mananara, Cóte Est , [16°10’S / 49°46’E], Oct. 1912, Perrier de La Bathie 5029 (P 05457228!, holo.; P 05457229!, iso.).

Description

Shrub up to ± 3.5 m tall. Branches reddish or brownish, beset with sparse lenticels; twigs glabrous. Leaves 1-foliolate, alternate; blade coriaceous, persistent, widely ovate or elliptic, (60–)70–140(–160) × (30–) 40– 93 mm, with entire margins; base attenuate or obtuse; apex acuminate, with tip up to ± 8 mm long, or acute, mucronulate; surfaces glabrous; nerves (4–)5–6(–8) on each side of the midrib; petiole (7–)12–41(50) mm long, glabrous, articulate at the top. Flowers in 7–16-flowered terminal, subsessile, dense subumbels or corymbs; pedicels 8–12 mm long, glabrous; bracts ± 0.5 mm long or lacking; flower buds (5.0–)5.5–8.0 × (4–) 5–8 mm, with whitish, ovoid or ellipsoid calyx at maturity rupturing transversally, the calyptra often remaining attached at one side; petals 0; androgynophore ± 1.0– 1.5 mm long; stamens ± 51 to 72, filaments 22–28 mm long, anthers 2.5 mm long; gynophore ± 25–26 mm long, glabrous; ovary oblong, ± 3–4 mm long, glabrous. Fruit ellipsoid, 45–63 × 29–45 mm, 8-ribbed; seeds ovoid, brownish, ± 13–18 × 10–11 mm. Figure 1 .

Distribution and habitat

The new species is known from two localities of the Analanjirofo Region ( Figure 2 ), at 16°10’S / 49°46’E and 15°40’S / 49°57’E, where it has been collected in coastal forest and in dense evergreen, humid forest, from sea level up to ± 300 m elevation. Based on the available material, flowering occurs in October, fruiting in April.

Etymology

The specific epithet is composed of the Latin words latum, meaning wide, and folium, meaning leaf.

Diagnosis and relationships

The new species is related to Thilachium madagascariense Fici , from which it differs in the coriaceous, widely ovate or elliptic, (30–) 40–93 mm wide leaf blade (leaf blade chartaceous, narrowly obovate or elliptic, (20–) 33–50 mm wide in T. madagascariense ); leaf apex with tip up to ± 8 mm long, mucronulate (tip up to 15 mm long, not mucronulate in T. madagascariense ); inflorescence a 7–16-flowered terminal, dense subumbel or corymb (2 or 3 flowers conferted at the top of lateral twigs in T. madagascariense ); pedicels 8–12 mm long (12–18 mm long in T. madagascariense ); and anthers 2.5 mm long (1.5–2.0 mm long in T. madagascariense ).

With regard to other species with 1-foliolate leaves from Madagascar, T. latifolium shows also affinities with T. laurifolium Baker , which differs from the former in the smaller, subemarginate leaf blade, 25–75 × 25–30 mm; inflorescence a 4–6-flowered terminal, loose corymb; pedicels (30–) 35–50 mm long, stamens ± 30–46 with filaments 31–35 mm long; and gynophore ± 50– 70(–80) mm long. Among the 1-foliolate species of the genus recorded from eastern Africa, T. latifolium is closer to T. thomasii Gilg , a species widespread in Kenya and southern Somalia (Elffers et al. 1964), which is distinguished by the petiole (4–)5–9(–14) mm long; leaf blade with apex obtuse or rounded, not acuminate; inflorescence a 1–10-flowered terminal, loose corymbose raceme; pedicels up to 20 mm long; and stamens ± 18–25.

Conservation status

Lacking information to assess its risks, Thilachium latifolium is assessed here as Data Deficient (DD). However, it is to be underlined that one of the known localities falls within a conservation area (Masoala National Park).

Other material examined

MADAGASCAR, Analanjirofo Region: Park National de Masoala, Andranobe , Fok. Ambanizana, Fir. Anjahana, Fiv. Maroantsetra, 15°40’S / 49°57’E, 200–300 m, 17 Apr. 1996, Aridy et al. 260 (MO, P 04746459) .

Notes

Apart from the widely ovate or elliptic leaves with apex shortly acuminate, Thilachium latifolium is mainly differentiated from the other 1-foliolate species of the genus in Madagascar by its terminal, dense subumbels or corymbs. The inflorescence in Thilachium is commonly reported as a terminal, axillary or on short lateral branches, corymbose raceme (Elffers et al. 1964; Kers 2002), or more rarely 2 or 3 flowers are conferted at the apex of lateral twigs ( Fici 2021a). Among the known species a dense, many-flowered corymb is reported only for T. densiflorum Gilg & Gilg-Ben. , a 3-foliolate species from Tanzania, with buds up to 5 mm in diameter and receptacle elongating to ± 8 mm at anthesis (Elffers et al. 1964). As mentioned above T. latifolium shows some affinities with T. madagascariense , a species recently described from eastern Madagascar, and with T. laurifolium , known from the central and eastern parts of the island ( Hadj Moustapha Haddade 1965; Fici 2021a; Anon 2022). A key to the species of Thilachium known from Madagascar is here provided.

Madagascar constitutes a centre of speciation of the genus Thilachium , which is represented here by nine endemic species, besides one species also native to eastern Africa and one to Mauritius; among these, five species have 1-foliolate leaves and six species 3-foliolate leaves. The description of this new species confirms that the historical herbarium collections still represent a remarkable and inspiring source of data for plant taxonomists ( Fici 2021a) in areas such as eastern Madagascar.

Figures

Figure 1. Thilachium latifolium. A, flowering branch; B, flower bud; C, flower; D, fruit and stipe. A, B, C from Perrier de La Bathie 5029 (holotype), D from Aridy et al. 260. Artist: Silvio Fici.

Figure 2. Distribution of Thilachium latifolium.