Christiana restingae T. S. Cout., Barb. Silva & Dorr 2025, sp. nov.
Creators: name: Coutinho, Thales Silva
name: Barbosa-Silva, Rafael G.
name: Dorr, Laurence J.
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Malvales
Malvaceae
Christiana
Christiana restingae

description: 5.Christiana restingaeT. S. Cout., Barb. Silva & Dorr sp. nov.
Figs 1 E, F, 2, 4, 5
Type.
Brazil. Espírito Santo: Vila Velha, Interlagos, 20 Jun 1996 (fr), O. Zambom & M. Fernandes 286 (holotype: VIES [VIES 010759]!).
Diagnosis.
Christiana restingae resembles C. mennegae but can be distinguished by its elliptic (vs. narrowly elliptic, lanceolate, or oblanceolate) leaf blades, calyces with stellate only (vs. stellate and glandular) trichomes, and capsules with inconspicuous (vs. conspicuous) wings.
Description.
Trees, 4–11 m tall, functionally dioecious. Branches whitish, cylindrical, rugose, lenticels circular to oblong, 0.5–1 mm long, old branches glabrescent, trichomes stellate-multiradiate, sessile, ferrugineous, sparsely distributed, stipules caducous. Leaves alternate, spirally arranged; petioles 1.3–3 cm long, discolorous when compared to the branches, vinaceous, inconspicuously striate, not canaliculate, terete, not decurrent, sparsely pilose, trichomes stellate-multiradiate, ferrugineous, more concentrated near the branches; leaf blades entire, coriaceous, nitid when dry, concolorous to quickly discolorous, 5.5–13.5 × 3–7 cm, elliptic, bases round to subcordate, margins plane, entire, apices acuminate to cuspidate, glabrous or glabrescent above and below, but with stellate-multiradiate trichomes sparsely distributed along the veins, and glandular-sessile trichomes on the blade below; venation actinodromous, 6–8 pairs of secondary veins, 2 pairs basal, impressed above, prominent below. Inflorescences axillary, umbellate with flowers attached to peduncles; bracts caducous; peduncles whitish, striate, 5–5.5 cm long, glabrous to glabrescent, trichomes sparse. Floral buds globose, ca. 2.5 × 2.5 mm. Flowers functionally unisexual; bracteoles c. 3.5 × 0.9 mm, elliptic, abaxial surface pubescent; pedicels 1.8–2 mm long, densely pubescent, trichomes stellate-multiradiate, ferrugineous, sessile. Pistillate flowers: calyx gamosepalous, 5 - merous, cupuliform, c. 4.5 mm long, with apical lobes free, pubescent abaxially, trichomes stellate-multiradiate, lobes c. 2.5 × 2 mm, ovate, apex acute. Corolla dialypetalous, 5 - merous, white, petals c. 2.8 × 1.3 mm, obovate, glabrous, apices rounded. Androecium polystemonous, staminodes 1.4–2 mm long, filaments 1.2–1.8 mm long, glabrous, anthers c. 0.3 mm long, divergent. Gynoecium 5 - carpellate, ovary ca. 1.2 × 1 mm, depressed globose, densely pubescent, trichomes stellate-multiradiate, style hirsute, trichomes stellate-multiradiate, stigma not observed. Staminate flowers: not observed. Fruit a capsule, woody, syncarpous, c. 1.5 cm long, 1.3–1.7 cm diam., depressed-globose, 4–5 - locular, inconspicuously winged, c. 0.6 × 0.6 mm, densely pubescent abaxially, glabrous, lustrous internally; seeds 1 per locule, 5 × 4 mm, ellipsoid, variegated, gray with brownish marks, glabrous.
Distribution and habitat
(Fig. 2). Christiana restingae is known only from Espírito Santo state, in Vila Velha and Presidente Kennedy municipalities, and in the northeast of Rio de Janeiro state. This is the only species of the genus occurring in the state of Espírito Santo. The new species is found in the Atlantic Forest phytogeographic domain, where it grows in Dense Ombrophylous Forest, as well as in Restinga, at 5–300 m elevation.
The Brazilian coast has an intense history of plant collecting, especially in the coastal region of the states of Espírito Santo and Rio de Janeiro. Recently, Dutra et al. (2022) with the Espírito Santo Flora Project strengthened floristic and taxonomic studies in the state, including new collections in Restinga areas (Guarnier et al. 2022).
Phenology.
Flowering specimens collected in January and fruiting in January, May, June, and August.
Conservation status.
Christiana restingae could be assessed as Endangered (EN) because its EOO is 1,230 km 2 (<5,000 km 2) or Critically Endangered (CR) because its AOO is 8 km 2 (<10 km 2). The IUCN (2012) recommendation is that the taxon be classified under the highest threat category. We therefore consider the species Critically Endangered (CR) under B 2 ab (i, ii, iii) criteria. In addition, C. restingae grows in Atlantic Forest and Restinga, vegetation types with an intense history of deforestation and human occupation.
Vernacular name.
Guaxumbão.
Etymology.
The specific epithet refers to Restinga, vegetation typical of the Brazilian coast, characterized by sandy soil, where the new species is usually found.
Paratypes.
Brazil. Espírito Santo: Presidente Kennedy, 21 ° 16 ' 07 " S, 040 ° 57 ' 58 " W, 5 m elev., 12 Aug 2020 (fr), A. M. Assis & R. S. Cribari 4899 (VIES). Vila Velha, Convento da Penha, 300 m, 11 May 2007 (fr), D. A. Folli 5755 (CVDR [digital image], US [01317134]); ibid., 300 m, 11 Sep 2009 (fr), D. A. Folli 6409 (CDRV [digital image], US [01317133]); Vila Velha, Interlagos, 22 May 1996 (fr), O. Zambom & M. Fernandes 283 (VIES), ibid., 31 Jan 1996 (fl, im fr), O. Zambom et al. 222 (VIES). Rio de Janeiro: Armação de Búzios, 31 Aug 2003 (fr), H. C. Lima et al. 6114 (MBM [digital image], NY [03987289], RB [digital image]); São Francisco de Itabapoana, Estação Ecológica de Guaxindiba, 17 Jul 2018 (fr), H. C. Lima et al. 8683 (RB, 2 sheets [digital images]); Rio das Ostras, Jul 2004 (fr), A. Oliveira & D. Oliveira 1016 (RB).
SEM.
The abaxial surface of the leaves has many sparse glandular trichomes and adjacent to the veins near the base it has stellate-multiangulate trichomes (Fig. 5 A, B). The abaxial surface of the epidermis has cells shaped like irregular polygons (Fig. 5 B). The epicarp has stellate multiangulate trichomes (Fig. 5 C).
The seed has several openings and crevices (Fig. 5 D, E) and its surface has small sparse papillae (Fig. 5 F).
Discussion.
Christiana restingae is described here three decades after it was first collected by O. Zambom and M. Fernandes. Ironically, it is worth mentioning that most of the large botanical research centers in Brazil are concentrated in the central region of the Atlantic Forest, and this is where most Brazilian plant taxonomists are based. This underscores the lack of attention Christiana has received in recent years (Barbosa-Silva et al. 2021) and the paucity of specialists knowledgeable about certain groups of plants.
Christiana is a genus with homogeneous morphology, sharing stellate trichomes on the vegetative and reproductive parts including inflorescences and flowers. Using a Scanning Electron Microscope (SEM), Barbosa-Silva et al. (2021) discovered the occurrence of simple, two-armed, and glandular trichomes on the petioles and leaf blades of C. mennegae, characters known only from this species. Leaf shape and capsule morphology can be useful to distinguish the different species. Christiana africana, the most widespread species of the genus, has an apocarpic gynoecium and fruit, which is an apomorphy. On the other hand, C. macrodon is the only species with leaf blades that are serrate along the entire length of their margins. Analyzing the type of C. vescoana, it was observed that in a few specimens the leaf blades near the apex also have this leaf margin characteristic, albeit less pronounced.
Christiana restingae is characterized especially by its elliptic leaf blades and fruits with inconspicuous wings. It has the shortest leaf length among the species of the genus, with mature leaf blades as small as 5.5 cm long. The new species differs from C. africana and C. macrodon by its elliptic leaf blade with rounded to subcordate (vs. widely cordate and cordate) bases. It also is distinguished from C. africana by its syncarpous (vs. apocarpous) capsules and from C. macrodon by leaf blades with entire (vs. dentate) margins. Although, morphologically, the new species is more similar to C. mennegae in having nitid leaves when dried, glabrescent, and with trichomes especially on the veins, C. restingae is distinguished by having smaller leaf blades (5.5–13.5 × 3–7.5 vs. 12.3–29 × 5–9 cm) that are elliptic (vs. narrowly elliptic, lanceolate or oblanceolate), and capsules 1.3–1.7 cm in diam. and with inconspicuous wings (vs. 3.8 cm in and conspicuous wings).
The analysis of structures in SEM brings new insights into understanding the genus, which exhibits various characteristics that can aid in species differentiation. For instance, the leaves of Christiana restingae possess more glandular trichomes than C. mennegae and have stellate-multiangulate trichomes, whereas C. mennegae only has stellate rotate trichomes on its leaves (Barbosa-Silva et al. 2021). Additionally, with SEM, the cell walls of the epidermis of C. restingae are visible, a character not seen in C. mennegae. The epicarp of C. restingae also exhibits a high concentration of stellate-multiangulate trichomes similar to C. mennegae. The seed of C. restingae also has maculae that are medium brown with darker irregular marks like other species in the genus; however, only C. restingae has these openings and crevices (Fig. 5 E), which even can be observed in herbarium material without the aid of magnification. Although these openings and fissures have been found in all fruit-bearing material, we are not sure if they are found in fresh material or if this character occurs only during the drying process of specimens. The seed of C. restingae does not have stomata, a character that was found to be very interesting in C. mennegae and is also present in other Malvaceae species, although it is rare in Angiosperms (Paiva et al. 2006; Barbosa-Silva et al. 2021).
Regarding geographic distribution, Christiana restingae is endemic to Espírito Santo and Rio de Janeiro states, occurring in Atlantic Forest and Restinga, sharing the vegetation type with C. africana (Amazonia and Atlantic Forest) and C. macrodon (Atlantic Forest and Cerrado) (Coutinho 2025). Christiana mennegae and C. restingae do not occur sympatrically since the first species occurs in Brazil only in the Amazonian Domain (Secco 2000; Barbosa-Silva et al. 2021). With the discovery of Christiana restingae, the number of species of the genus in Brazil reaches four, making the country the center of diversity. Of the six known species of the genus, two are endemic to Brazil and its Atlantic Forest.
It is worth noting that with the Flora do Brasil 2020 project (BFG 2021), various taxonomists were encouraged to monograph different groups. Consequently, plant groups that had long gone without taxonomic revisions, that were neglected, or that were known to be of little interest, were revised. Thus, numerous results have been published in recent years as a result of this careful process of revision in these groups (Giulietti 2020; Andrino et al. 2022; Antar et al. 2022; Asprino et al. 2024; Barbosa-Silva 2024). The same factor also has driven recent studies on the genus Christiana (Barbosa-Silva et al. 2021), as well as the data presented here.
description: Published as part of Coutinho, Thales Silva, Barbosa-Silva, Rafael G. & Dorr, Laurence J., 2025, A synopsis of Christiana DC. (Malvaceae, Brownlowioideae), with a new species from the Brazilian Atlantic Forest, pp. 33-56 in PhytoKeys 253 on pages 33-56, DOI: 10.3897/phytokeys.253.145350