6. Croton celtidifolius Baillon (1864: 331) .

Lectotype (designated by Santos et al. 2017): — BRAZIL. Rio de Janeiro: s.d., A. Saint-Hilaire s.n. (P 00623096!, isolectotypes P 00623095!, SP 417993!) . Remainimg syntypes: — BRAZIL. Rio de Janeiro: P.C.D. Claussen s.n. (P n.v., W n.v.); Serra dos Órgãos, 1833, M. Vauthier 93 (G-DC 00311468!, GH 00257899!, MPU 014851!, P 00493362!, P 00493363!, SP 000651!, W 0051195!); Serra dos Órgãos, 1838, G. Gardner 618 (P 00493364!, P 00493365!, P 00493366!, NY 00246524!, NY 00246523!, K 000186059!, US 00109521!, W 0051196!, W 1889-013284!) (Fig. 3, F–K).

Croton celtidifolius is a small to medium sized tree. It has a pair of stipitate acropetiolar nectary glands, the staminate flowers are long pedicellate with ca. 60 stamens, and the styles are tetrafid. This species is very similarly to C. vulnerarius, however these species can be differentiated by stamen numbers (ca. 60 in C. celtidifolius vs. 80–130 in C. vulnerarius), pistillate flower aestivation and pedicel length (valvate and pedicellate in C. celtidifolius vs. imbricate and subsessile in C. vulnerarius), styles (free in C. celtidifolius vs. basally connate in C. vulnerarius) and capsule ornamentation (slightly verrucose in C. celtidifolius vs. smooth in C. vulnerarius). Croton celtidifolius also resembles Croton urucurana, from which it can be differentiated by its nectary glands (stipitate acropetiolar in C. celtidifolius vs. sessile basilaminar in C. urucurana), stamens number (ca. 60 in C. celtidifolius vs. ca. 20 in C. urucurana) and style division (tetrafid in C. celtidifolius vs. bifid in C. urucurana). The species belongs to Croton sect. Cyclostigma Grisebach (1859: 42) (van Ee et al. 2011).

Distribution and habitat:— It occurs in southern (PR, RS, SC) and southeastern Brazil (ES, MG, RJ, SP) (Santos et al. 2017, Caruzo et al. 2020). Trees growing on edges of Araucaria forest, Atlantic rainforest and riparian forest, between 800 and 990 m elevation (Fig. 4).

Phenology:— Flowering and fruiting from October to May.

Representative specimens:— PARANÁ: Adrianópolis, Parque Estadual das Lauráceas, 11 January 2000, I . Isernhagen et al. 308 (MBM, UPCB). Campo Largo, Bateias, 03 January 1978, G . Hatschbach 41075 (MBM, NY). Piraí do Sul, Rod. Governador Parigot de Souza, próximo ao km 247, sentido Jaguariaíva, 20 October 2016, A. P. N . Pereira, O. L. M . Silva & F. S . Petrongari 38 (SP). Quatro Barras, 900 m, 20 January 1999, O. V . Doria, A. A . Carpanezzi & W . Maschio 01 (ESA, HFC, HUEM). Tijucas do Sul, Ribeirão do Mel, 10 January 1992, O. S . Ribas & E . Barbosa 401 (HUEFS, MBM, W) .