Savassi-Coutinho, A.P., Lewis, G.P. & Souza, V.C. Kew Bull (2012) 67: 827. https://doi.org/10.1007/s12225-012-9417-x
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Type
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Typus: Brazil, Mato Grosso do Sul, Mun. Naviraí, Savassi-Coutinho & Coutinho 1253 (holotypus ESA!; isotypi CGMS!, K!, MBM!, NY!, P!, RB!, SPF!).
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Morphology
General
Habit
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Erect shrubs, 1 – 3 m tall
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Morphology
Branches
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Branches striate; branches, petioles, leaf axes and peduncles hirsutulous with plumose (Fig. 1B) and penicillate trichomes, trichomes 1 – 2 mm long, epidermis partially visible or obscured by the trichomes, not glabrescent
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Morphology
Leaves
Stipules
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Stipules linear-lanceolate, 5 – 15 × 0.5 mm, 1-veined, hirsutulous on both surfaces, not ciliate, persistent
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Morphology
Leaves
Petiole
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Petioles 1.3 – 3 cm long; pinnae 1-jugate, leaf-axis extending beyond pinnae as a 3 mm long projection; leaflets in 8 – 14 pairs per pinna, rachis of pinna 5 – 10.3 cm long, extending beyond the terminal leaflets as a 2 mm long projection, leaflets increasing in size towards the pinna apex or the largest leaflets in the middle of the pinna, the basal pair 1 – 4 mm distant from the subulate or setiform, 2 mm long and persistent paraphyllidia, the leaflet blades elliptic, oblong or oblanceolate, acute to obtuse at the apex, oblique at the base (the proximal side rounded, the distal side acute), the margin not thickened, 1.1 – 2 × 0.5 – 0.7 cm, concolorous, 4-veined from the base on both surfaces (the outer anterior vein weak and expiring ⅓ of the way up the blade surface, the inner anterior vein and the displaced midrib extending strongly to, or just below, the apex, the posterior vein weak and expiring ⅔ up the blade surface), leaflet blades pubescent on both surfaces, the upper surface covered by stellate trichomes and the lower surface by penicillate and plumose trichomes, the surface of the blade visible amongst the trichomes (Fig. 1C, D, E and F)
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Morphology
Reproductive morphology
Inflorescences
Peduncles
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Peduncles 0.7 – 2.7 cm long; flowers in cylindrical spikes, these either solitary or grouped into fascicles of 1 – 4 and these further aggregated into an indeterminate thyrse, the individual spikes (excluding the expanded filaments) 0.9 – 1.5 × 0.3 – 0.6 cm; bracts longer than flower buds, linear, 1.3 – 1.5 × 0.1 – 0.2 mm, moderately covered above the middle or just at the apex by stellate-setose trichomes, not ciliate, the bracts persisting at the fruit bases; flowers 4-merous, all bisexual; calyces cupuliform, 0.2 – 0.3 mm long, truncate, with no apparent lobes, ciliolate at the apex, tube glabrous; corolla campanulate, 1.8 – 2.5 mm long, tube covered by simple, retrorselyadpressed trichomes, surface visible amongst the trichomes, lobes covered at the apex by longer plumose trichomes (Fig. 1H, J, K and L); stamen filaments white to pink coloured, 3.5 – 5.5 mm long, exserted beyond the corolla by 2.5 – 3 mm, united basally for 0.5 mm, with or without staminodia; ovary 0.4 – 0.8 mm long, covered by sessile stellate trichomes, style glabrate, stigma narrow, porate, equalling the style in width
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Morphology
Reproductive morphology
Fruits
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Immature craspedium 1 × 0.4 cm, hirsutulous, covered by ferruginous, plumose trichomes, epidermis obscured by the trichomes (Fig. 1G), mature articles and seeds not seen.
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Distribution
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Brazil: Mato Grosso do Sul. Map 1.
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Ecology
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In swamps and flood plains, alt. 246 – 523 m.
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Conservation
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IUCN (2001) category Endangered, EN B1a + biii. Mimosa roseoalba is endangered because there are now only three fragmented populations, covering an area of less than 5,000 km2 (approximately 3,500 km2). Although each population comprises hundreds of individuals they are located in a very threatened habitat with no native vegetation surrounding it, only areas of pasture (where the natural vegetation has been converted into agricultural land).
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Phenology
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Collected in flower in Oct. and Feb. and in immature fruit in Feb.
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Note
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The specific epithet roseoalba alludes to the colour of the stamen filaments that are white at anthesis and become pink with age.
Mimosa roseoalba is also very similar to M. diversipila var. diversipila (belonging to section Mimosa ser. Mimosa subser. Brevipedes), a species that also sometimes has branched trichomes, although these, when present, are only microscopically branched. M. diversipila var. diversipila was included as one of 28 Mimosa taxa analysed by Bessega et al. (2008) in their preliminary analysis of southern South American species of Mimosa based on chloroplast DNA sequences. They suggested that the plumose indumenta present in several infrageneric groups of Mimosa could be considered as being due to evolutionary convergence. In addition, M. diversipila var. diversipila is a virgate shrub with shorter petioles (2 – 7 mm long), the penicillate trichomes are absent on the whole plant, the heads are globose and not longer than 7.5 mm, the corolla tube is glabrous and the corolla lobe apices are covered with a few short simple trichomes. According to Barneby (1991) M. diversipila var. diversipila is a locally common taxon in eastern Paraguay south of the Apa River and east of the Paraguai River and extends just west of the latter into extreme eastern Formosa, Argentina. In Brazil, M. diversipila var. diversipila has been reported from the western portion of southern Mato Grosso do Sul, in ‘Serra do Amambaí’ (Barneby1991), where it can apparently occur sympatrically with M. roseoalba. However, no collection of M. diversipila var. diversipila from this Brazilian locality has been found in any of the herbaria visited by the first author.
Mimosa roseoalba is morphologically similar to M. plumosa and M. crassipesArechav. However, in M. plumosa the branch, petiole, leaf-axis and peduncle indumentum is hirsute with a mixture of plumose-setose, plumose and sessile stellate trichomes (not hirsutulose with only plumose and penicillate trichomes), the stipules are lanceolate and wider (1 – 2 mm wide) and the flowering spikes larger (2 – 3 × 0.6 – 1 cm). M. crassipes has stipitate-stellate trichomes on the leaflet upper surface, the flowers are arranged in globose heads and the corolla tube is covered by sessile stellate trichomes.
Mimosa roseoalba is a dominant species on flood plains of the south region of Mato Grosso do Sul and can be easily identified, even when in leaf only, by its hirsutulous indumentum on the branches, petioles, leaf-axes and peduncles, by leaves with only one pair of pinnae and by penicillate trichomes on the leaflet upper surface. In flower there are also very good diagnostic characters such as the presence of plumose trichomes on corolla lobe apices and the stamen filaments that change from white to pink with age.
