Naiadendron A.G. Lima, Paula-Souza & Scalon, 2022

de Lima, Alexandre G., de Paula-Souza, Juliana, Ringelberg, Jens J., Simon, Marcelo F., de Queiroz, Luciano P., Borges, Leonardo M., de F. Mansano, Vidal, Souza, Vinicius C. & Scalon, Viviane R., 2022, New segregates from the Neotropical genus Stryphnodendron (Leguminosae, Caesalpinioideae, mimosoid clade), PhytoKeys 205, pp. 203-237 : 203

3. Naiadendron A.G. Lima, Paula-Souza & Scalon gen. nov.

Type.

Naiadendron duckeanum (Occhioni f.) A.G. Lima, Paula-Souza & Scalon ≡ Stryphnodendron duckeanum Occhioni f., Revista Brasil. Biol. 19: 209. 1959 ).

Diagnosis.

Naiadendron is closely related to Stryphnodendron , but it differs in having strongly striate branches (vs. smooth or only slightly striate in Stryphnodendron ), a petiolar nectary 8-12 mm long (vs. 0.5-2 mm long), leaflets inserted in opposite pairs (vs. alternate pairs), fruit a legume, valves dehiscing along both sutures (vs. fruit an indehiscent, nucoid legume or follicle). The genus differs from Piptadenia in having unarmed branches (vs. armed branches in Piptadenia ) and ferruginous granular trichomes on branches and leaves (vs. ferruginous granular trichomes absent).

Description.

Trees 8-30 m tall; branches unarmed, strongly striate, castaneous, apex yellow-tomentose and covered with ferruginous granular trichomes, not odoriferous. Stipules caducous. Leaves bipinnate, petiole yellow-puberulent or yellow-tomentulose, sparsely covered with ferruginous granular trichomes, petiolar nectary 1, 8-12 mm long, narrowly oblong, positioned at the base of the petiole; rachis 10-23 cm long, yellow-puberulent or yellow-tomentulose, sparsely covered with ferruginous granular trichomes, rachis nectary 1, ca. 2 mm long, oblong, inserted below the distal pair of pinnae; pinnae in 10-22 subopposite to opposite pairs, rachilla nectary 1, 1 × 0.4 mm, oblong, secretory, inserted below the distal pair of leaflets; leaflets in 15-23 opposite pairs, 0.6-1.2 × 0.3-0.5 cm, oblong, elliptic or sometimes obovate, no tuft of trichomes at the base on the abaxial surface, not odoriferous. Inflorescence a simple thyrse formed by cymules of 3-5 spikes, spike 4-7 cm long (peduncle plus rachis), covered with ferruginous granular trichomes, spike prophyll caducous, flower prophyll usually caducous. Flowers monoclinous; calyx pentamerous, gamosepalous, ca. 0.5 mm long, campanulate, puberulent; corolla pentamerous, gamopetalous, 1.8-2 mm long, cohered for ⅓ of its length, narrow-campanulate, yellow-tomentulose; androecium with 10 stamens, anthers with a caducous apical gland. Fruit a legume (dehiscent along both margins), peduncle 1.3-2 cm long, fruit body 12-15 × 2-2.5 cm, linear to narrow-oblong, laterally-compressed sparsely covered with ferruginous granular trichomes, chartaceous, brown. Seeds obovate to elliptic, ochre colored. Fig. 3 .

Geographic distribution and habitat.

Naiadendron is endemic to the Amazon rainforest, being recorded from the Brazilian states of Acre, Amazonas and Rondônia. It grows on clay or sandy soil in ombrophilous and terra firme forests (Fig. 9 ).

Etymology.

The name Naiadendron celebrates the Amazon rainforest and the legacy of Carl Friedrich Philipp von Martius (1794-1868), who named the Brazilian Amazon after the Naiads, Greek mythology’s nymphs of freshwater.

Notes.

Strongly striate branches, a petiolar nectary 8-12 mm long, and the fruit a legume (valves dehiscing along both margins) are the main diagnostic morphological characteristics of Naiadendron .

Occhioni (1959) described Stryphnodendron duckeanum , based only on flowering specimens, and pointed out its morphological similarity to S. guianense . However, both morphological ( Scalon 2007; Lima et al. 2021; Scalon et al. 2022) and phylogenetic evidence ( Simon et al. 2016; Ribeiro et al. 2018) have indicated that S. duckeanum should be recognized as an independent taxon, now named as the new genus Naiadendron .

Figures

Figure 3. A, B Microlobius foetidus: A fruiting branch with white seeds exposed B detail of a leaflet showing the tuft of trichomes at the base of the midrib C-G Naiadendron duckeanum: C fruits D detail of the striated branch E detail of petiolar nectary (upper view, magnified) F bark slash showing reddish exudate G flowering branch. Photos: A Donovan Bailey B Alexandre Gibau de Lima C-G Marcelo Simon.

Figure 9. Distribution of Naiadendron duckeanum.