Mimozyganthus Burkart, Darwiniana 3: 448. 1939.
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https://dx.doi.org/10.3897/phytokeys.240.101716 |
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persistent identifier |
https://treatment.plazi.org/id/41118F44-29AB-CE78-2C62-49D96EBFC4EA |
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scientific name |
Mimozyganthus Burkart, Darwiniana 3: 448. 1939. |
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Mimozyganthus Burkart, Darwiniana 3: 448. 1939. View in CoL
Figs 144 View Figure 144 , 146 View Figure 146 , 154 View Figure 154
Type.
Mimozyganthus carinatus (Griseb.) Burkart [≡ Mimosa carinata Griseb.]
Description.
Shrub or small treelet, 3-5 m (Fig. 144H View Figure 144 ), armed with stipular spines at nodes; young branches zigzagging, glabrate to finely puberulent, brachyblasts present, clothed with persistent stipules and bearing leaves and inflorescences. Stipules linear and firm on young growth, forming spines on older branches. Leaves bipinnate, borne on brachyblasts or alternate on new growth, petiole shallowly canaliculate, terminating in a caducous spicule; rachis (if present) to 8 mm long; nectaries sessile, orbicular, crateriform, between all pairs of pinnae; pinnae 1-2 (3) pairs, opposite, articulate to the rachis, elongate red glands present at their insertion; leaflets 15-35 pairs per pinna, alternate to subopposite proximally, opposite distally, oblong. Inflorescences globose capitula borne in pairs or fours congested on the brachyblasts or axillary on new growth; bracteoles subtending each flower subulate, spiny and greatly exceeding the flowers in bud. Flowers all hermaphrodite, 25-35 per inflorescence, sessile; hypanthium absent; sepals 5, imbricate in bud, free to base, indurate and incurved at apex; petals 5, irregularly valvate in bud, sometimes valvate apically and imbricate basally, free, glabrous, greenish; stamens 10, free, anthers dorsifixed, lacking a terminal gland; intrastaminal disc absent; pollen in columellate tricolporate monads, exine verrucate, colpi granular; ovary ovoid, stipitate, glabrous, stigma large, peltate, sub-pentagonal. Fruits several per axis, indehiscent, elliptical, acute apically and basally, 3.5-4 × 1-1.5 cm, 1 (2)-seeded, dorsiventrally flattened, pericarp thin, papery, translucent when young, pale brown at maturity, ventral sutural rib flattened and forming a narrow wing (Fig. 146M View Figure 146 ). Seeds dorsiventrally compressed, orbicular in outline, narrowly winged, testa thin, pleurogram absent, chestnut brown.
Chromosome number.
2 n = 28 ( Luckow et al. 2005).
Included species and geographic distribution.
Monospecific ( M. carinatus ), centred on the Chaco phytogeographic region in north-west and west-central Argentina, north-west Paraguay and south-east Bolivia (Fig. 154 View Figure 154 ).
Ecology.
Tropical and subtropical arid and semi-arid Chaco woodlands and adjacent Piedmont seasonally dry scrub and forest, 150-1200 m elevation. The papery marginally-winged fruits suggest that the fruit is likely wind-dispersed.
Etymology.
From Greek, zygo - (= paired) and - anthos (= flower), referring to the inflorescences which arise in the yoke between a pair of spinescent stipules, plus the Greek prefix mimo - (= mime or mimic) indicating placement of the genus in what was then subfamily Mimosoideae .
Human uses.
Used locally for firewood and lumber; apparently a dye can be extracted from the stems ( Fortunato 2005).
Notes.
Until recently, Mimozyganthus was sometimes considered to be ‘transitional’ between subfamily Caesalpinioideae and the former Mimosoideae and was placed in its own tribe Mimozygantheae ( Burkart 1939; Fortunato 1997, 2005). This placement of Mimozyganthus was based on three characters more typical of non-mimosoid Caesalpinioideae than of genera of the mimosoid clade: imbricate, as opposed to valvate, aestivation of the sepals, a peltate stigma, and lack of a pleurogram on the seed. However, molecular phylogenetic analyses ( Luckow et al. 2005; Koenen et al. 2020a; Ringelberg et al. 2022) have shown that this monospecific genus is indeed a mimosoid, placed in a robustly supported subclade with Prosopidastrum and Piptadeniopsis within the Dichrostachys clade sensu Koenen et al. (2020a). This placement requires an evolutionary reversal in sepal aestivation. Lack of a pleurogram is best understood as an adaptation often seen in phylogenetically scattered hydrochorous and anemochorous Caesalpinioideae . Although this subclade is geographically coherent in being almost entirely distributed in the Argentinian-Paraguayan-Bolivian Chaco domain and shares similar armature (spinescent stipules) across its three constituent genera, there is remarkable diversity in floral and pollen morphology suggesting strong selection for floral diversity across this subclade. The peltate stigma in Mimozyganthus is apparently similar to the anvil-shaped, flanged stigma of Kanaloa , although very limited material of Kanaloa with fertile flowers is available.
Taxonomic references.
Burkart (1939); Luckow et al. (2005), both with illustrations.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.
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SubFamily |
Caesalpinioideae |
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Tribe |
Mimoseae |