Heliodendron Gill.K. Br. & Bayly, 2022

Brown, Gillian K., Aju, Javier, Bayly, Michael J., Murphy, Daniel J. & McLay, Todd G. B., 2022, Phylogeny and classification of the Australasian and Indomalayan mimosoid legumes Archidendron and Archidendropsis (Leguminosae, subfamily Caesalpinioideae, mimosoid clade), PhytoKeys 205, pp. 299-333 : 299

Heliodendron Gill.K. Br. & Bayly gen. nov.

Fig. 5

Diagnosis.

A genus of mimosoid legumes similar to Archidendropsis but differing in the following combination of features: inflorescences of glomerules, calyx and corolla with hairs (restricted to the lobes in H. xanthoxylon ); stipules either small (to 1.2 mm) rigid and caducous or glandular (1.2-3 mm long) and persistent; pollen arranged in polyads diameter of 55-68 μm; pollen tectum with isometric channels. In contrast, Archidendropsis has inflorescences of spikes, spiciform racemes, racemes or in one species glomerules, but when in glomerules the calyx and corolla are glabrous; stipules (if present) either small (c. 1mm) ovate or filiform and often caducous, or large auriculate, orbicular, or cordate and persistent; pollen polyad diameter of 80-120 μm, pollen tectum with non-isometric channels.

Description.

Trees or shrubs, with terete branchlets. Stipules either resembling small thorns to 1.2 mm long that are early caducous, or persistent circular-ovate glands 1-3 mm in diameter. Leaves bipinnate, pinnae 1-2 pairs with 1.5-11 leaflet pairs per pinna; glands at the junction of pinnae circular or triangular to rhombic, +/- circular glands at the junction of leaflet petiolules. Leaflets opposite, subsessile (0.2-0.7 mm) or long (3.5-7 mm) petiolulate; elliptic to elliptic-lanceolate or oblong, 2-38 mm × 1.5-15 mm, glabrous to puberulous. Inflorescence of globular heads 0.5-1.7 mm in diameter, either simple or arranged into a panicle up to 35 cm long. Flowers: homomorphic, yellow to cream, sessile. Calyx 1.5-3 mm long, tubular to subcampanulate; corolla 2.5-7 mm long, tubular to narrowly campanulate. Ovary 0.8-2 mm long, solitary and shortly stipitate; stamens numerous 5-9 mm long, united basally into a tube that equals or slightly exceeds the corolla tube. Pollen 16-celled polyads with a diameter of 55-68 μm, tectum with isometric channels. Pod brown, valves chartaceous, 6-22 cm × 0.5-2.5 mm, oblong, flat and dehiscing along both sutures. Seeds lacking a pleurogram, flat, circular to ovate or obliquely ovate, 5-13 mm, with a narrow 0.2-1 mm peripheral, membranous wing. Fig. 5 .

Type.

Heliodendron basalticum (F. Muell.) Gill.K. Br. & Bayly ≡ Acacia basaltica F. Muell., Journal of the Proceedings of the Linnean Society, Botany 3: 146 (1859)

Etymology.

From the Greek helios (sun) and dendron (tree) alluding to the endemic distribution of the genus in the Australian state of Queensland, widely known as the "sunshine state", the globular, sun-like inflorescences of yellow flowers, and the tree habit (Fig. 5A, K, L ) and also in reference to the genera Archidendropsis (in which the species were previous placed) and Archidendron (which they resemble).

Homotypic synonym.

Archidendropsis subg. Basaltica I.C. Nielsen, Bulletin du Muséum National d’Histoire Naturelle. Section B, Adansonia : Botanique Phytochimie 5(3): 325 (1983).

Notes.

We have chosen to create a new name for this genus rather than making a new combination based on the name Archidendropsis subg. Basaltica . This is because using the name " Basaltica " at generic rank would require a change of epithet for the most widespread species in the genus under Art. 23.4 of the International Code of Nomenclature for algae, fungi, and plants ( Turland et al. 2018). To minimise taxonomic change, and to avoid potential confusion, we would rather that the species retains its well-known epithet, which has been in continuous use since 1859.

The genus includes the following three species, all endemic to Queensland, Australia (Fig. 1B ).

Figures

Figure 1. Distribution maps of the genera Archidendron and Archidendropsis. The maps are based on quality-controlled species-level digitised herbarium specimens from GBIF (www. gbif. org) (Ringelberg et al. 2022). Maps were created using R packages ggplot 2 (Wickham 2016), sf (Pebesma 2018), and rnaturalearth (South 2017) A Archidendron. Species distributions are coloured according to the ncDNA phylogeny clades (Fig. 2) except for A. clypearia: Clade E (Clypeariae clade) = green dots; clade F (Archidendron s. s. clade) = blue dots; species not sampled for the phylogeny = red dots. Archidendron clypearia is widespread and falls in both clades E and F, so for this species locations of samples in the ncDNA phylogeny are coloured according to their clade and all other records of this species are coloured red. The overall distribution of series Clypeariae is shown by a blue dashed line B Archidendropsis. All species that belong to subg. Archidendropsis are coloured red and those in subg. Archidendron Basaltica (= Heliodendron gen. nov.) are coloured orange.

Figure 5. Morphology of Heliodendron. Plate showing diagnostic features of the new genus Heliodendron A inflorescence of H. thozetianum, Hazelwood Gorge, west of Mackay, Queensland (photo, Stuart Worboys, Australian Tropical Herbarium) B single flower of H. basalticum (BRI AQ 0648454) showing hairs on calyx and corolla C mature bud of H. xanthoxylon (BRI AQ 0874091) showing hairs on the lobes of the calyx and corolla D seeds of H. basalticum (BRI AQ 0746724) E overall pod shape of H. xanthoxylon (BRI AQ 0234095) F small rigid stipules of H. basalticum (BRI AQ 0673898) G glandular stipule of H. xanthoxylon (BRI AQ 0771148). Whole leaf showing overall leaflet size and shape of H H. basalticum (BRI AQ 0648454) I H. thozetianum (BRI AQ 0611464), and J H. xanthoxylon (BRI AQ 0874091). Habit of H. basalticum from K Bladensberg National Park, Queensland (photo, Dale Richter, Queensland Herbarium) L 65 km west south-west of Blackall, Queensland (photo, Murray Fagg, Australian Plant Image Index, Australian National Botanic Gardens).