Mariosousa Seigler & Ebinger, Novon 16(3): 415. 2006.

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

Mariosousa Seigler & Ebinger, Novon 16(3): 415. 2006.

Figs 192 , 195

Type.

Mariosousa coulteri (Benth.) Seigler & Ebinger [≡ Acacia coulteri Benth.]

Description.

Unarmed shrubs and trees; bark hard and fissured or scaly, sometimes papery and exfoliating; brachyblasts normally absent (except commonly present in M. compacta (Rose) Seigler & Ebinger). Stipules small, mostly persistent, not spinescent. Leaves bipinnate, not sensitive; extrafloral nectaries present on petiole and/or rachis (petiole glands commonly absent in M. gentryi Seigler & Ebinger, M. millefolia (S. Watson) Seigler & Ebinger and M. salazarii (Britton & Rose) Seigler & Ebinger), sessile or occasionally stipitate; pinnae 1-20 (30) pairs; paraphyllidia present or absent; leaflets opposite, (4) 8-65 pairs per pinna. Inflorescences comprising pedunculate, loosely flowered spikes, 1-4 in leaf axils or arranged in short, normally terminal, racemose clusters; peduncles lacking a multi-bracteate involucre. Flowers hermaphrodite, uniform, 5-merous, with a basal nectariferous disk, sessile, creamy white; perianth connate, valvate, not scarious; stamens numerous (50+), free; anther glands normally present; pollen comprising 16-grained polyads, porate and lacking pseudocolpi, exine surface rugulate, exine lacking columellae; ovary stipitate. Fruits dehiscent along both sutures, strongly flattened, valves chartaceous or coriaceous. Seeds exarillate, not winged, pleurogram U-shaped (open at hilar end) and areole usually large (covering 50%-70% of the seed) (Fig. 192A-G ).

Chromosome number.

Unknown.

Included species and geographic distribution.

Fourteen species distributed from Arizona and New Mexico (one species), south through Mexico (where all species of the genus occur) to Belize, Guatemala, El Salvador, Honduras, Nicaragua and Costa Rica (where three species occur, the most widespread being M. centralis (Britton & Rose) Seigler & Ebinger) (Fig. 195 ).

Ecology.

Mainly in seasonally dry tropical forests, thorn-scrub and thickets, weakly extending into moister semi-deciduous tropical forests; on arid hills or sometimes rocky deserts or desert grasslands, 0-2200 m elevation.

Etymology.

The genus Mariosousa honours Mario Sousa (1940-2017), legume specialist and former Director of the Herbarium of the Instituto de Biología (MEXU), Universidad Nacional Autónoma de México.

Human uses.

Mariosousa coulteri is one of the few trees of this genus with enough size and quality of wood to be of some local importance and useful for lumber ( Seigler and Jones 2005). The wood is extremely durable and is sought after for building houses.

Notes.

Immediately prior to the description of Mariosousa , the 13 species that were subsequently assigned to this genus were included in the informal Acacia coulteri species-group ( Jawad et al. 2000). Before that, many species had been treated as Senegalia by Britton and Rose (1928) or as Acacia by Bentham (1875) under the Nudiflorae group of subseries Americanae Spiciflorae ; this group also included some species now assigned to both Parasenegalia and Senegalia . Mariosousa together with Parasenegalia (and Pseudosenegalia ) are distinguished from Senegalia by their lack of prickles. Mariosousa is further distinguished from Senegalia by the order of development of seedling leaves: those of Mariosousa having the first two leaves pinnate followed by a bipinnate leaf, whereas in Senegalia the first three leaves are bipinnate or a singly pinnate leaf followed by two bipinnate leaves ( Vassal 1972). A key that includes these four genera is provided in Miller et al. (2017).

Phylogenetic analyses of plastid and/or nuclear sequence data have supported the genus as monophyletic ( Seigler et al. 2006a, 2006b; Miller et al. 2017). Jawad et al. (2000) had previously used morphometric studies to revise the group and included a key to species and formal descriptions. Seigler et al. (2006a, 2006b) also provided a key to the then recognised 13 species of Mariosousa , but an additional species, M. gentryi , was described by Seigler and Ebinger (2021).

Mariosousa heterophylla (Benth.) Seigler & Ebinger [= Acacia willardiana Rose, ≡ Mariosousa willardiana (Rose) Seigler & Ebinger], which is endemic to the state of Sonora, Mexico, is morphologically somewhat unusual, but is clearly nested within Mariosousa (fide Seigler et al. 2006a, 2006b). Apart from its exfoliating, papery bark (which also occurs in M. gentryi and M. salazari ) the exceptionally long flattened petioles (2-40 cm) that normally support a single pair of pinnae are highly distinctive within the genus. Bentham (1846) noted these characters and commented that the petiole was 'almost phyllodinous’ when he tentatively assigned this taxon to Prosopis heterophylla Benth. Vasey and Rose (1890) subsequently referred this species to Acacia , as A. willardiana ; a proposal by Seigler and Ebinger (2008) to conserve this name against P. heterophylla was declined ( Brummitt 2011; Barrie 2011). Vassal and Guinet (1972) conducted a detailed study of the phyllodinous petioles of A. willardiana which they described as being horizontally flattened, and as such applied the term ‘diaphyllode’ to them. Bentham (1846) had erroneously described the phyllodes as vertically flattened ( ‘orthophyllodes’), which is the normal condition found in species of Acacia . However, diaphyllodes do occur in few disparate groups of Australian Acacia ( Vassal and Maslin 1979). Note that pollen data are only available for two species of Mariosousa , namely, M. centralis and M. coulteri ( Guinet 1969; Caccavari and Dome 2000; Rico Arce and Banks 2001; Duarte et al. 2021).

Taxonomic references.

Bentham (1846, 1875); Britton and Rose (1928); Jawad et al. (2000); Miller et al. (2017); Nielsen (1992); Seigler et al. (2006a, 2006b, 2023); Seigler and Ebinger (2008, 2021); Vasey and Rose (1890); Vassal (1972).

Figures

Figure 192. Morphology of Mariosousa, Parasenegalia and Pseudosenegalia A Mariosousa acatlensis (Benth.) Seigler & Ebinger spicate inflorescences (Seigler 16002) B M. coulteri (Benth.) Seigler & Ebinger bark not papery C M. dolichostachya (S. F. Blake) Seigler & Ebinger branchlet unarmed (Seigler 16035) D-F M. salazari (Britton & Rose) Seigler & Ebinger D exfoliating papery bark (Seigler 16057) E habit F fruits (Seigler 15978) G M. usumacintensis (Lundell) Seigler & Ebinger leaf (Seigler 16027) H Pseudosenegalia feddeana (Harms) Seigler & Ebinger fruits (Atahuachi 1146) I, J Parasenegalia miersii (Benth.) Seigler & Ebinger (Terra, Coutinho & Dalvi 667) I branch showing unusual leaves (i. e., pinnae few and leaflets large) J inflorescences K Pseudosenegalia feddeana contorted tree habit. Photo credits A-G B Maslin H, K CE Hughes I, J V Terra.

Figure 195. Distribution of Mariosousa based on quality-controlled digitised herbarium records. See Suppl. material 1 for the source of occurrence data.