Heliodendron Gill.K. Br. & Bayly, PhytoKeys 205: 321. 2022.

Bruneau, Anne, de Queiroz, Luciano Paganucci, Ringelberg, Jens J., Borges, Leonardo M., Bortoluzzi, Roseli Lopes da Costa, Brown, Gillian K., Cardoso, Domingos B. O. S., Clark, Ruth P., Conceicao, Adilva de Souza, Cota, Matheus Martins Teixeira, Demeulenaere, Else, de Stefano, Rodrigo Duno, Ebinger, John E., Ferm, Julia, Fonseca-Cortes, Andres, Gagnon, Edeline, Grether, Rosaura, Guerra, Ethiene, Haston, Elspeth, Herendeen, Patrick S., Hernandez, Hector M., Hopkins, Helen C. F., Huamantupa-Chuquimaco, Isau, Hughes, Colin E., Ickert-Bond, Stefanie M., Iganci, Joao, Koenen, Erik J. M., Lewis, Gwilym P., de Lima, Haroldo Cavalcante, de Lima, Alexandre Gibau, Luckow, Melissa, Marazzi, Brigitte, Maslin, Bruce R., Morales, Matias, Morim, Marli Pires, Murphy, Daniel J., O'Donnell, Shawn A., Oliveira, Filipe Gomes, Oliveira, Ana Carla da Silva, Rando, Juliana Gastaldello, Ribeiro, Petala Gomes, Ribeiro, Carolina Lima, Santos, Felipe da Silva, Seigler, David S., da Silva, Guilherme Sousa, Simon, Marcelo F., Soares, Marcos Vinicius Batista & Terra, Vanessa, 2024, Advances in Legume Systematics 14. Classification of Caesalpinioideae. Part 2: Higher-level classification, PhytoKeys 240, pp. 1-552 : 1

Heliodendron Gill.K. Br. & Bayly, PhytoKeys 205: 321. 2022.

Figs 226 , 227 , 228 , 235

Archidendropsis subg. Basaltica I.C. Nielsen, Bull. Mus. Natl. Hist. Nat., B, Adansonia Sér. 4, 5(3): 325. 1984. Type: Archidendropsis basaltica (F. Muell.) I.C. Nielsen [≡ Acacia basaltica F. Muell. (≡ Heliodendron basalticum (F. Muell.) Gill.K. Br. & Bayly)]

Type.

Heliodendron basalticum (F. Muell.) Gill.K. Br. & Bayly [≡ Acacia basaltica F. Muell.]

Description.

Trees or shrubs to 37 m. Stipules either resembling small thorns to 1.2 mm long that are caducous, or persistent circular-ovate glands 1-3 mm in diameter. Leaves bipinnate; extrafloral nectaries at junction of pinnae circular or triangular to rhombic, circular glands sometimes at junction of leaflet petiolules; pinnae 1-2 pairs; leaflets 1.5-11 pairs per pinna, opposite, subsessile or long (3.5-7 mm) petiolulate, elliptic to elliptic-lanceolate or oblong. Inflorescence capitula, either simple or arranged into a panicle to 35 cm long. Flowers uniform, bisexual, 4- or 5-merous, yellow to cream, hairy, sessile; calyx gamosepalous, tubular to subcampanulate, symmetrical; corolla gamopetalous, tubular to narrowly campanulate; stamens numerous, united basally into a tube that equals or slightly exceeds the corolla tube; pollen in 16-celled polyads, tectum with isometric channels; ovary solitary and shortly stipitate. Fruits brown, valves chartaceous, oblong, flat and dehiscing along both sutures. Seeds lacking a pleurogram, flat, circular to ovate or obliquely ovate, with a narrow 0.2-1 mm peripheral, membranous wing.

Chromosome number.

Unknown.

Included species and geographic distribution.

Three species restricted to the state of Queensland in Australia (Fig. 235 ).

Ecology.

One species [ H. xanthoxylon (C.T. White & W.D. Francis) Gill.K. Br. & Bayly] is found in rainforest remnants on granitic soils whereas the other two species [ H. basalticum and H. thozetianum (F. Muell.) Gill.K. Br. & Bayly] are found in drier habitats on sandy to sandy-clay loam soils, either in eucalypt woodland, acacia shrubland or semi-deciduous vine thickets.

Etymology.

From helios (Greek = sun) in reference to the endemic distribution in the Australian state of Queensland, widely known as the "sunshine state", and to the capitate, sun-like inflorescences of yellow flowers, and dendron (Greek = tree) to the tree habit.

Human uses.

Heliodendron has been used as timber for general building and the manufacture of window frames, cabinets, barrels and boat building ( Swain 1928).

Notes.

Heliodendron was newly described for the morphologically distinct Archidendropsis subg. Basaltica after phylogenetic studies found the two subgenera of Archidendropsis to be non-monophyletic ( Brown et al. 2022). The rainforest H. xanthoxylon has larger leaflets and fewer leaflets per pinna than the two drier habitat species, but they all share the diagnostic features of the genus (inflorescences in capitula, seeds flat, lacking a pleurogram and with a narrow peripheral membranous wing, calyx and corolla with hairs, pods narrowly oblong, brown, opening along both sutures, pollen polyad diameter of 55-68 μm and pollen tectum with isometric channels) and there would be little benefit in separating H. xanthoxylon as a monospecific genus.

Taxonomic references.

Brown et al. (2022); Cowan (1998); Nielsen (1981a).

Figures

Figure 226. Habit and leaf morphology diversity in genera of the Archidendron clade A Archidendron clypearia (Jack) I. C. Nielsen B Heliodendron thozetianum (F. Muell.) Gill. K. Br. & Bayly C Falcataria falcata (L.) Greuter & R. Rankin D Heliodendron basalticum (F. Muell.) Gill. K. Br. & Bayly E Serianthes kanehirae Fosberg var. kanehirae F Serianthes kanehirae var. yapensis Fosberg G Pararchidendron pruinosum (Benth.) I. C. Nielsen H Paraserianthes lophantha subsp. montana (Jungh.) Benth. with tomentose stems and leaves I Wallaceodendron celebicum Koord. Photo credits A C Ng B R Cumming C J Teo D D Richter E, F JB Friday G G Brown H F and K Starr I Plantoholic Sheila.

Figure 227. Inflorescence and flower diversity of genera in the Archidendron clade A Archidendron vaillantii (F. Muell.) F. Muell. B Archidendropsis paivana (E. Fourn.) I. C. Nielsen C Falcataria falcata (L.) Greuter & R. Rankin D Heliodendron thozetianum (F. Muell.) Gill. K. Br. & Bayly E Serianthes sp. F Pararchidendron pruinosum (Benth.) I. C. Nielsen G Paraserianthes lophantha (Willd.) I. C. Nielsen H Wallaceodendron celebicum Koord. Photo credits A, F A Furhmann B B Henry C JB Friday D S Worboys E T Rodd G AndyBonsai H Plantaholic Sheila.

Figure 228. Fruit and seed diversity of genera in the Archidendron clade A fruit of Archidendron lucyi F. Muell. (Brown 169) B open pod of Archidendropsis streptocarpa (E. Fourn.) I. C. Nielsen showing winged seeds C opened pod of Falcataria falcata (L.) Greuter & R. Rankin D Heliodendron xanthoxylon (C. T. White & W. D. Francis) Gill. K. Br. & Bayly opened pod (Hyland 9229) E Heliodendron basalticum (F. Muell.) Gill. K. Br. & Bayly winged seeds (Canning & B. Rimes 6173) F-H Serianthes dilmyi Fosberg showing the indehiscent (to very tardily dehiscent) (rarely) woody pods with transverse seeds which are each isolated in a chamber I Pararchidendron pruinosum (Benth.) I. C. Nielsen fruit and seedling J Paraserianthes lophantha (Willd.) I. C. Nielsen immature pods (Brown 204 A) K Wallaceodendron celebicum Koord. pod. Photo credits A, I, J G Brown B B Henry C JB Friday D, E Queensland Herbarium F-H R CJ Lim K Plantaholic Sheila.

Figure 235. Distribution of Heliodendron based on quality-controlled digitised herbarium records. See Suppl. material 1 for the source of occurrence data.