Prosopidastrum Burkart, Darwiniana 13(2-4): 436. 1964.
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publication ID |
https://dx.doi.org/10.3897/phytokeys.240.101716 |
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persistent identifier |
https://treatment.plazi.org/id/88BBDEBA-A492-97B8-4750-D0B37B567BFA |
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treatment provided by |
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scientific name |
Prosopidastrum Burkart, Darwiniana 13(2-4): 436. 1964. |
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Prosopidastrum Burkart, Darwiniana 13(2-4): 436. 1964. View in CoL
Figs 144 View Figure 144 , 145 View Figure 145 , 146 View Figure 146 , 155 View Figure 155
Type.
Prosopidastrum mexicanum (Dressler) Burkart [≡ Prosopis globosa var. mexicana Dressler]
Description.
Small often aphyllous shrubs, 0.5-1.5 (3) m (Fig. 144I View Figure 144 ), usually armed with spinescent stipules, the shoots also often spinescent, tapered to a hard point, the whole shrub prickly; stems green, photosynthetic, striate with longitudinal, golden corky ridges (Fig. 145G View Figure 145 ); plants usually glabrous, sometimes sparsely pubescent with simple hairs. Stipules spinescent, straight or recurved, persistent or sometimes caducous, each bearing a rounded, adaxial nectary. Leaves bipinnate, small, to 2 cm long; nectaries cylindrical to cupulate, pitted, borne between the pinnae; pinnae 1 pair, opposite; leaflets 1-4 pairs per pinna, opposite, sessile, venation obscure except for central midvein. Inflorescence a capitulum, axillary, one head per axil (Fig. 145G View Figure 145 ); bracteoles subtending each flower peltate to lanceolate, hooded. Flowers 5-merous, sessile or pedicellate, functionally staminate or bisexual; sepals valvate in bud, connate, calyx campanulate, shallowly lobed; petals valvate in bud, free or basally adnate to the stamens forming a stemonozone, 1-veined, variously reflexed or incurved; stamens 10, fertile, filaments not flattened, white, anthers ovate, dorsifixed, pale yellow, equipped with a stipitate claviform apical gland; intrastaminal nectaries present; pollen in columellate tricolporate monads; ovary short stipitate to sessile, glabrous to pilose, stigma punctate with a deep cup. Fruit dorsiventrally flattened, linear-oblong loments (Fig. 146L View Figure 146 ) or craspedia, rarely dehiscent along the ventral suture, 3-10-seeded; valves coriaceous, exocarp light brown, reticulately veined, forming an umbo over each seed, endocarp smooth, fibrous, mesocarp absent, layers of fruits not separating from one another at maturity. Seeds not winged, obliquely inserted, testa hard, pleurogram present.
Chromosome number.
2 n = 14, 28 ( Luckow et al. 2005).
Included species and geographic distribution.
Six to eight species occupying a highly disjunct amphitropical distribution in Baja California and Isla Socorro, Mexico and central Argentina (Fig. 155 View Figure 155 ).
Ecology.
In arid subtropical scrub and semi-desert vegetation. Often aphyllous. Fruits breaking up into one- or few-seeded segments.
Etymology.
From - astrum (Latin = partial resemblance to) and Prosopis , another mimosoid genus which it resembles.
Human uses.
Unknown.
Notes.
Prosopidastrum shares with Piptadeniopsis and Mimozyganthus , the two genera with which it is resolved in a robustly supported subclade of the Dichrostachys clade (Fig. 143 View Figure 143 ; Luckow et al. 2005; Koenen et al. 2020a; Ringelberg et al. 2022), spinescent stipules and a mainly Argentina - Paraguay - Bolivia Chaco - Monte distribution in South America. Prosopidastrum is of particular biogeographic interest, being disjunct between Baja California and Argentina.
In the past, only 1-2 species were recognised until Palacios and Hoc (2001, 2005) worked on the Argentinian members when they recognised six species in Argentina alone. The main characters they used to separate species include sessile vs. pedicellate flowers, fruit dehiscent or indehiscent, and texture of the leaflets, as well as branching pattern and persistence of the stipules. A secondary character was inflorescence size.
It is difficult to reliably distinguish P. angusticarpum R.A. Palacios & Hoc from P. striatum (Benth.) R.A. Palacios & Hoc as the diameter of the inflorescence does not correlate with other characters, all of which overlap except petal colour and pubescence. The status of the segregates P. gracile R.A. Palacios & Hoc and P. benthami (Chodat & Wilczlek) R.A. Palacios & Hoc is also doubtful as they appear to differ from one another only in the colour of the petals (white vs. green-tipped). Thus, pending more detailed taxonomic revisionary work, there is uncertainty about whether six or eight species should be recognised in the genus.
Taxonomic references.
Palacios and Hoc (2001, 2005), with illustrations.
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