Croton bacupariensis Valduga & Iganci, 2021

Valduga, Eduardo, Cordeiro, Inês & Iganci, João Ricardo Vieira, 2021, Croton bacupariensis (Euphorbiaceae), a new species from the Coastal Plain of Rio Grande do Sul, Brazil, Phytotaxa 528 (4), pp. 240-246 : 241-243

Croton bacupariensis Valduga & Iganci , sp.nov. ( Figures 1 , 2 )

Type: — BRAZIL. Rio Grande do Sul: Mostardas, Lagoa do Bacopari , 30°32’19.98”S 50°25’21.93”W, 29 May 2017 (fl), E . Valduga 795 (holotype ICN! isotypes HUCS!, ICN!)

Diagnosis: —Densely branched shrub up to 60 cm tall, monoecious. Croton bacupariensis is very similar to C. gnaphalii Baillon (1864: 359) , but differs mainly by its densely branched shrubby habit (vs. sparsely branched in C. gnaphalii ); stellate-lepidote trichomes on the abaxial surface of leaves (vs. stellate trichomes on both surfaces in C. gnaphalii ); pistillate sepals 2.3 mm long (vs. 4.2 mm long in C. gnaphalii ). Table 1 .

Monoecious shrubs, 30–60 cm tall, densely branched; branches cylindrical to flattened in the apex, covered by cream to silver indument of stellate-lepidote trichomes; latex translucid. Leaves elliptic slightly discoloured, without petiolar colleters; lamina 4–12 × 2–5 mm, apex acute, base acute to obtuse, margin entire, abaxial surface pubescent with silver stellate-lepidote trichomes with ferruginous to brownish spots, adaxial surface with silver stellate trichomes, hiphodromous, central vein immersed on the adaxial surface and prominent abaxially, secondary veins inconspicuous; petioles 0.8–1 mm long, covered by subentire lepidote trichomes. Staminate inflorescences 0.7–1.5 cm long, terminal, lax, axis covered by stellate-lepidote trichomes; bracts ca. 3.6 mm long, linear lanceolate, glabrate on the adaxial surface, covered by stellate-lepidote trichomes on the abaxial one. Staminate flowers: pedicel 1.5–3.5 mm long; sepals 5, valvate, entire, ca. 3 × 1.5 mm, narrowly ovate, apex slightly cucullate, entire, adaxial surface glabrate, abaxial one with stellate trichomes; petals linear, narrowly elliptic, ca. 3 × 1 mm, ciliate; adaxial surface glabrate and abaxial one with stellate trichomes; receptacle covered by simple and hyaline trichomes; nectary disk segmented; stamens ca. 15; filaments hirsute. Pistillate inflorescences: 5–10 mm long, terminal, lax, axis covered by stellate-lepidote trichomes; pedicels ca. 3 mm long. Pistillate flowers: sepals 5, valvate, ca. 2.3 × 1.2 mm, narrowly ovate, entire, adaxial surface glabrescent with sparse stellate-lepidote trichomes, abaxial with stellate-lepidote trichomes; reduced petals linear, ca. 0.5 mm long; ovary ca. 1.6 × 1.4 mm, trigonous, covered by stellate-lepidote trichomes; styles bifid (with 12 terminal tips), covered by stellate-lepidote trichomes; nectary disk deeply 5-lobed. Capsules ca. 5 × 4.2 mm, ellipsoid. Seeds 3.3 × 2.1 mm, narrowly ellipsoid, brownish; caruncle tiny, ca. 1.5 × 0.4 mm, reniform, yellowish.

Distribution and Habitat — Croton bacupariensis has been collected so far in the Brazilian State of Rio Grande do Sul ( Fig. 3 ), in open vegetation on sandy soils of dunes near the sea level, around lagoons.

Phenology —Flowers and fruts found in January, May and October.

Paratypes — BRAZIL. Rio Grande do Sul: Mostardas, Lagoa do Fundo, 15 January 2008 (stam. fl), L. Scur 1191 (HUCS!, MBM!); Mostardas, Lagoa do Bacupari, 30°32’32”S 50°25’02”W 05 October 2018 (stam. fl.), C. Rabuske-Silva & C.C. Alff 379 (ICN!).

Etymology —The specific epithet refers to the type-locality, Praia do Bacupari, in the Municipality of Mostardas, Rio Grande do Sul, Brazil.

Suggested Conservation Status — Croton bacupariensis could be considered Critically endangered (CR) according to the IUCN (2017) criteria B1 b(I,ii,iii,iv,v)C1. Its area of occupation (AOO) is 8.000 km ² and only two populations of the species were found on sandy soil in the municipality of Mostardas, around salt lagoons, an area that is rapidly being occupied by real estate development.

Comments —While Croton bacupariensis is restricted to the sandy soils of the dunes, near lagoons in the municipality of Mostardas, Rio Grande do Sul state, C. gnaphalii is widely distributed in the Pampa’s grasslands, in Argentina, Uruguay and Rio Grande do Sul, in Southern Brazil, growing mostly in rocky soils. Croton bacupariensis is here classified in Croton sect. Lamprocroton due to the presence of a lepidote indumentum,leaves without petiolar glands, and bifid styles with four terminal tips. The following species occur in the same environment: Croton lombardianus Croizat (1942:1) , which is distinct by having branches predominantly prostrate, serrate leaves and stellate trichomes (vs. ascending branches, entire leaves and stellate-lepidote trichomes in C. bacupariensis ). Croton lombardianus was recently recorded to Brazil by Valduga et al. (2021). Croton glandulosus Linnaeus (1759: 1275) is distinguished by the serrate leaves and stipitate glands at the base of the leaf blade, or at the apex of the petiole (vs. entire leaves without glands in C. bacupariensis ). Croton helichrysum Baillon (1864: 358) is recognized by the spatulate leaves (vs. elliptic leaves in C. bacupariensis ) and Croton lanatus Lamarck (1786: 211) presents sessile glands at the base of the leaf (vs. leaf glands absent in C. bacupariensis ).

Figures

FIGURE 1. Croton bacupariensis. A. Habit; B. Stellate-lepidote trichomes from abaxial leaf surface; C. Staminate flower; D. Pistillate flower; E. Fruit (all Valduga 795).

FIGURE 2. Croton bacupariensis. A. Habitat; B. Immature fruit; C. Staminate flower; D. Pistillate flower; E. Leaves. Photos A, C, D by Eduardo Valduga, B, E by Martin Grings.

FIGURE 3. Distribution map of Croton bacupariensis, showing the only two localities where the species was collected until now in the Rio Grande do Sul state, Brazil.