Idimanthus amorphophalloides E. G. Gonc. 2018, sp. nov.
Creators: name: Gonçalves, Eduardo G.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Liliopsida
Alismatales
Araceae
Idimanthus
Idimanthus amorphophalloides

description: Idimanthus amorphophalloides E.G. Gonç., sp. nov. (Figs. 1, 2)   
 Type:— BRAZIL. Rio de Janeiro: Italva, Quimbira, em mata semidecídua, 7 December 2013, Costa, I. G. 276 (holotype RB).   
 Geophyte herb in deciduous forest. Stem tuberous, hypogeous, tuber 1.0–1.2 × 1.5–2.0 cm, producing 2–3 lanceolate cataphylls; roots numerous, whitish, 1–4 mm diam, appearing mostly at the apex of the tuber. Leaves: cataphylls, 0.8– 1.0 × 0.2–0.3 cm, foliage leaf with petiole 2–5 × 0.2–0.3 cm, pale green, inconspicuously sheathed only at base, leaf blade ovate-sagittate overal dimensions 5–7 × 4.5–6.0 cm, semi-glossy medium green adaxially, matte and withish, anterior division 4.5–5.6 × 4.5–6.0 cm, primary nerves 2–3 per side, arising at an angle of 42–50 o, interprimary nerves poorly visible, higher order venation reticulate, posterior divisions 1.5–2.3 × 2.2–3.0 cm, acroscopic veins 1–3, basiscopic veins 0–2, basal costa denuded by 1–3 mm. Inflorescences appearing before leaves, peduncle 1.0–1.3 × 0.2–0.4 cm, Spathe broadly ovate to subcordate, 2–3 × 1.2–1.5 cm, weakly cymbiform, acuminate and rostrate at apex, off-white to pinkish beige, sometimes with shades of grey, reticulated with reddish nerves. Spadix up to 4 cm long, apical staminoidal portion densely flowered, 1.8–2.0 × 0.1–0.5 cm, cylindrical, greyish brown to yellowish brown, round at apex, weakly to strongly dimorphic, 3–5 rows of basal staminodes usually larger than apical ones, fertile male portion densely flowered, 0.8–2.0 × 0.2–0.4 cm, conical to barrel shaped or cylindrical, 1.2–1.3 × 0.2–0.4 cm, usually concolorous with staminoidal portion or a little clearer, female portion densely flowered, 0.7–0.9 × 0.2–0.4 cm, barrelshaped, about 3/4 adnate to the spathe, yellowish cream. Apical sterile flower fungus shaped, 1-androus but sometimes appearing as an amorphous synandrium. Male flower 1-androus, each comprising a short filament, 3–5 × 0.3–0.6 mm, mm, thecae globose, ca. 0.3 mm diam., opening by an apical round pore, connective flattened, somewhat irregular, ending in a rostrate beak turned downward. Female flowers barrel shaped, greenish white, 1.0–1.5 × 0.3–0.5 mm, stigma button shaped, yellowish at anthesis, ochre after, 1.0– 1.4 cm diam., covered by short trichomes, style 0.3–0.4 × 0.3 mm, ovary regular or obliquely disposed, c. 0.5–0.6 × 1.0– 1.5 mm, 1-loculed, 1-ovuled, ovule anatropous, funicle covered by trichomes. Fruit a spongy utricle, white, obovate, 0.7–0.8 cm. Seed ovoid, 0.5–0.9 × 0.3–0.4 cm, tegument coppery brown, thin, endosperm copious, embryo straight.   
 Etymology:— The specific epithet aludes the resemblance with a miniature specimen of the aroid genus Amorphophallus, mainly because of its peculiar habit of flowering much before any sight of the leaves.   
 Phenology:— Flowers from July to early November, fruiting briefly in late November to January.   
 Distribution and habitat:— So far known only from the forests fragments in a single marble outcrop in the county of Italva, very close to the city of Cardoso Moreira, as an understory geophyte. Although there are three different collections described in this protologue, they all were collected in the the same restricted locality.   
 Preliminary conservation status:— Based on the IUCN criteria and subcriteria B1,a, the species is here considered critically endangered (CR). Although the outcrop itself has been somewhat protected from the economic use of soil (mostly cattle farms in that area) in recent years, similar outcrops are locally explored by quarrying (Gonçalves & Salviani 2001, Gonçalves & de Paula 2016).   
 Morphological remarks:— Idimanthus is most similar to Filarum, a monotypic genus from Amazonian Peru.They share the cormous stem, variegated leaf blade (seen mostly in wild collected plants) and spadix with contiguous female and fertile male portion. Moreover, both genera seemed to prefer soils derived from basic stones, since Idimanthus grows in marble outcrop, whereas the region where Filarum was collected, Pongo de Manseriche, is a gorge excavated through the limestone by the Marañon river (Stephenson 1952). However, they differ in connective structure, since it is irregularly flattened with a beak turned downwards and much shorter than the filament in Idimanthus whereas it is filiform and much longer than the filament in Filarum.   
 Ulearum, a genus from western Amazon, should also be compared. Morphologically, they have in common the presence of cordate–sagittate leaves usually variegated with silvery blotches. However, they differ in important aspects. The most remarkable difference is that the seeds in Idimanthus have copious endosperm whereas it is absent in Ulearum. The stem is also very distinct, being cormose in Idimanthus and cleary rhizomatous in Ulearum. Both aspects seems to reflect the habitat diferences, since Idimanthus occur in an area with a mild but remarkable dry season whereas Ulearum usually does not experience noticeable seasonal variation in western Amazon. The inflorescence is also distinct, since Ulearum usually has a basal whorl of staminodes below the fertile male flowers, whereas they are absent in Idimanthus.   
 Only considering the inflorescence morphology, Idimanthus presents more resemblance with the also western Amazonian Zomicarpella, including the inflorescence with fertile male flowers contiguous with the female flowers, and with an apical spadix composed of fused staminodes. However, Idimanthus has a cormous stem, whereas the stem is a tuberous rhizome in Zomicarpella. Moreover, the fertile male flowers are sessile in Zomicarpella and there is a noticeable filament in Idimanthus flower.   
 As far as we know, the presence of the connective ending in a rostrate beak turned downward between the thecae, seems to be only found in this genus within the Caladieae. Together with the combination of cormous geophytic stem, copious endosperm and sterile flowers densely arranged in an apical appendix, Idimanthus did not match any other genera in the tribe.   
 Unpublished phylogenetic analysis of the entire tribe Caladieae (to be published elsewhere) shows that this monotypic Idimanthus only clusters as sister with the two species of Ulearum, in a clade that is significantly isolated from other studied genera. Considering the Western Amazonian genus as the closest relative of Southeastern Idimanthus, it would be interesting to investigate if their divergence is early in the evolution of the tribe or is the result of a more recent connection.   
 Cultivated material:— Idimanthus can be cultivated in well drained soil, but should be kept in pots much larger than usual geophytes. Despite it has a clear dormancy period, the corms tend to dry out when resting, and dries out even when kept in small amounts of soil. A larger pot will slow down the loss of water during dormancy, allowing the plant to rest properly. Adding limestone to the mix can improve growing and stimulate strongly variegated leaves.   
 Additional specimens examined (paratypes):— BRAZIL. Rio de Janeiro:Italva, Morro Quimbira, 21 o 27’31,4’’S – 41 o 35’38,83’’W, 100 m elev., December 2010, Peixoto, M. 15063 (UB). Italva, localidade de Quimbira, em mata a leste da Serra do Pão de Ló. 100 m elev., 22 July 2011, Costa, I.C. 187 (UB). Italva, localidade Quimbira, em mata semidecídua. 7 December 2013, Costa, I.C. 276 (RB).
description: Published as part of Gonçalves, Eduardo G., 2018, Idimanthus: A new aroid genus (Araceae-Caladieae) from Rio de Janeiro State, Brasil, pp. 88-92 in Phytotaxa 351 (1) on pages 89-92, DOI: 10.11646/phytotaxa.351.1.8, http://zenodo.org/record/13690621