Sympetalandra Stapf, Hooker's Icon. Pl. 28: t. 2721. 1891.

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

Sympetalandra Stapf, Hooker's Icon. Pl. 28: t. 2721. 1891.

Figs 114 , 115 , 116

Type.

Sympetalandra borneensis Stapf

Sympetalandra is here considered a monogeneric lineage, whose relationship to other Mimoseae remains difficult to determine. Although historically considered a member of non-mimosoid Caesalpinioideae ( Stapf 1891; Polhill and Vidal 1981; Polhill 1994), when first included in a molecular phylogenetic analysis the genus was resolved as a member of the mimosoid clade in the plastid matK analyses presented by LPWG (2017), a position that is now supported in the phylogenomic analyses of Ringelberg et al. (2022). As with Chidlowia Hoyle, the genus occurs nested between the Adenanthera and Entada clades, but the relationships between these two genera and these two clades are not clearly resolved (Fig. 114 ), as evidenced by the very short branches and possible polytomy at the base of the Mimoseae .

Description.

Unarmed, small to medium-sized tree (to 30 m), buttressed. Stipules minute or caducous. Leaves bipinnate (Fig. 115A ), rarely parapinnate ( S. borneensis ), with 1-3 pairs opposite or subopposite pinnae; leaflets large and few, opposite, 3-6 pairs, pellucid glands present. Inflorescences dense, terminal and axillary racemes arranged in panicles towards the tip (Fig. 115C, D ); bracts persistent beyond anthesis; bracteoles absent at anthesis. Flowers (Fig. 115E ) small, 4 mm long, flower buds ovoid, crowded; pedicel ca. 1.2 mm, slender; calyx cup-shaped, hairy, with 5 small overlapping lobes, pellucid-glandular; petals 5 equal, imbricate, oblong, pellucid-glandular, joined at base; stamens 10, 5 long and 5 short in bud, free, adnate to petals at base; pollen in monads, spheroidal, ornamentation psilate to psilate-finely perforate ( Banks and Lewis 2009); ovary stipitate, 2-6-ovulate, style long. Fruit thickly woody, elongate to 70 cm, flattened but bulging strongly at the big oval seeds (marked by an open reticulum of nerves), tardily dehiscent; valves with visible seed chambers, 1-3 seeds (Fig. 115B ). Seeds orbicular to ellipsoid, testa osseous; funiculus less than 1 mm long; hilum concealed by funicular remnant; pleurogram absent.

Chromosome number.

Unknown, but recent phylogenomic analyses suggest the genus may be polyploid ( Ringelberg et al. 2022, 2023).

Included species and geographic distribution.

Five species [ S. borneensis , S. densiflora (Elmer) Steenis, S. hildebrandii Steenis, S. schmutzii Steenis, S. unijuga (Airy Shaw) Steenis] restricted to Malesia (Fig. 116 ): Sumatra, Malay Peninsula, Borneo, Philippines, Lesser Sunda Islands (Flores).

Ecology.

Lowland tropical forests. Sympetalandra densiflora , known as Kamatog, is considered near-threatened under the IUCN Red List in the Philippines.

Human uses.

The bark of S. schmutzii is used as a fish poison ( Lewis 2005b). The wood of S. densiflora is of good quality and used in house constructions and furniture (Energy Development Corporation 2020).

Etymology.

The generic name refers to the petals that are shortly connate at their base.

Notes.

Sympetalandra was placed in the Dimorphandra group of tribe Caesalpinieae by Polhill and Vidal (1981), Polhill (1994), Lewis (2005b), and suggested to have affinity with this group of genera by Stapf (1891), but has been resolved as part of the mimosoid clade in molecular phylogenetic and phylogenomic analyses ( LPWG 2017; Ringelberg et al. 2022). Although Sympetalandra lacks valvate petal aestivation, often considered a synapomorphy for core mimosoids, the genus has bipinnate leaves (paripinnate only in S. borneensis ), racemose or paniculiform inflorescences, and small and regular flowers reminiscent of Mimoseae . Van Steenis (1975) noted morphological similarities in inflorescences and flower type with the genus Adenanthera L. ( Adenanthera clade), and remarked on their very similar, almost equal, narrow petals. The monospecific African Chidlowia , which occurs in a similar phylogenetic position, also has flowers similar to those of Sympetalandra in which the base of the calyx, petals and stamens are joined and thickened into a structure simulating a hypanthium ( Hoyle 1932).

Sympetalandra is subtended by a relatively long branch in the phylogenomic studies of Ringelberg et al. (2022) who noted a significant number of gene duplications, suggesting that the genus is likely polyploid. The occurrence of polyploidy, and particularly allopolyploidy, could be a factor contributing to the gene tree conflict observed among Sympetalandra , Chidlowia and the Adenanthera and Entada clades, which are the four first-branching lineages of Mimoseae . Given the short branches separating these four lineages, the high levels of gene tree conflict, and the slightly different relationships between these lineages found in the phylogenomic analyses of Ringelberg et al. (2022) and Kates et al. (2024), the phylogenetic relationships of the early-diverging Mimoseae lineages might for now best be depicted as a polytomy.

Taxonomic references.

Hou (1996d); Stapf (1891); van Steenis (1975).

Figures

Figure 6. Generic relationships in tribe Ceratonieae. Left part of figure shows complete genus-level Caesalpinioideae phylogeny with the Ceratonieae indicated with a red rectangle. Branch lengths are expressed in coalescent units and terminal branches were assigned an arbitrary uniform length for visual clarity. Support for relationships is based on fractions of supporting and conflicting gene trees: pie charts show gene tree support and conflict per node (blue representing supporting gene trees, green gene trees supporting the most common alternative topology, red gene trees supporting further alternative topologies, grey gene trees uninformative for this node), and numbers above pie charts are Internode Certainty All support values [both calculated with PhyParts (Smith et al. 2015)]. If present, red numbers below pie charts are non-significant (i. e.> 0.05) outcomes of ASTRAL's polytomy test (Sayyari and Mirarab 2018), which tests for each node whether the polytomy null model can be rejected. Monophyletic genera are represented by single branches; see Suppl. material 2 for a phylogeny with all accessions. See Suppl. material 3 for gene tree support across the phylogeny. The phylogeny is a pruned version of the backbone phylogeny of Ringelberg et al. (2023), where full details of the data and phylogenomic analysis methods are presented.

Figure 114. Phylogenetic position of Sympetalandra and Chidlowia in tribe Mimoseae. For description of phylogeny and support values, see Fig. 6 caption (page 63).

Figure 115. Sympetalandra unijuga (Airy Shaw) Steenis A bipinnate leaves with opposite pinnae and opposite leaflets B fruit, Malaysia (Madani 83436) C flowers in bud and early anthesis D slender, branched inflorescences E close-up of flower. Photo credits A, C-E Digital Flora of the Philippines (Pelser et al. 2011) B Naturalis Biodiversity Center, https: // medialib. naturalis. nl / file / id / L. 2027025 / format / large (CC 0 - 1.0).

Figure 116. Distribution of Sympetalandra based on quality-controlled digitised herbarium records. See Suppl. material 1 for the source of occurrence data.