Research Article |
Corresponding author: Rodrigo Duno de Stefano ( roduno@cicy.mx ) Academic editor: Luciano de Queiroz
© 2022 Iván Tamayo-Cen, Benjamin M. Torke, José Enrique López Contreras, German Carnevali Fernández-Concha, Ivón Ramírez Morillo, Lilia Lorena Can Itza, Rodrigo Duno de Stefano.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Tamayo-Cen I, Torke BM, López Contreras JE, Carnevali Fernández-Concha G, Ramírez Morillo I, Can Itza LL, Duno de Stefano R (2022) Revisiting the phylogeny and taxonomy of the Pithecellobium clade (Leguminosae, Caesalpinioideae) with new generic circumscriptions. In: Hughes CE, de Queiroz LP, Lewis GP (Eds) Advances in Legume Systematics 14. Classification of Caesalpinioideae Part 1: New generic delimitations. PhytoKeys 205: 279-298. https://doi.org/10.3897/phytokeys.205.82728
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We present the most complete molecular phylogeny to date of the Pithecellobium clade of subfamily Caesalpinioideae. This neotropical group was informally recognised (as the Pithecellobium alliance) at the end of the 20th century by
Fabaceae, Ingeae, Ingoid clade, mimosoid, New World, phylogenetic systematic, taxonomy
In their seminal monographic treatment of the American synandrous mimosoid legumes,
The Pithecellobium clade consists of five genera: Pithecellobium, with 19 species, is the largest genus, followed by Havardia Small, with five species and Ebenopsis Britton & Rose, Painteria Britton & Rose and Sphinga Barneby & J.W. Grimes, each with three species. It is restricted to the tropics and subtropics of the New World, with species distributed from the southern United States and the Caribbean Islands to Peru and north-eastern Brazil. Its centre of species diversity lies in Mexico, which harbours all five genera and 18 species. The Antilles and South America each harbour eight species. Habitats include subtropical and tropical deciduous and semi-deciduous forests, thorny scrub, chaparral, desert grasslands and other xeromorphic vegetation, as well as coastal scrub and swamp forests, including mangroves. Amongst the American synandrous mimosoids, the clade is defined morphologically by sympodial growth, proleptic, dimorphic branches forming vegetative and/or reproductive short-shoots; spinescent stipules; buds protected by the adaxial side of the petiole; coeval or late-suppressed leaves; inflorescences with monomorphic flowers; and colporate non-equatorial pollen apertures (
The five genera differ from each other most obviously in pod and seed characters (
Summary cladogram based on maximum parsimony analyses of 29 morphological characters of the Pithecellobium clade (one of two trees resulting, the second involves differences in the internal topology of Painteria) from
To date, most molecular phylogenetic analyses that included species of the Pithecellobium clade have sampled single species of Ebenopsis, Havardia, Pithecellobium and Sphinga and no species of Painteria (e.g.
Two molecular phylogenetic studies had substantially greater sampling of species of the Pithecellobium clade. The first, published as an electronic supplement to
The second study (
Nevertheless, over half of the species of the Pithecellobium clade remain unsampled in these phylogenetic studies and, thus, knowledge of relationships within the group is still incomplete. Filling the sampling gaps is needed to establish a more robust phylogenetic framework for revising the classification of the group and, ultimately, for reconstructing its evolutionary history.
Here, we present the most comprehensively sampled molecular phylogenetic study of the Pithecellobium clade to date, based on analysis of sequences from nuclear ribosomal DNA regions. The following questions are addressed: 1) Are the Pithecellobium clade and its constituent genera monophyletic? 2) Does analysis of molecular data support the relationships amongst and within the genera recovered by previous analysis of morphology (
The ingroup sample included multiple representative species of all five genera of the Pithecellobium clade, for a total of 20 of the 33 species (61%) of the group (Table
Voucher information and GenBank accession numbers for the DNA sequences used in the present study.
ETS | ITS | |
---|---|---|
outgroup | ||
Calliandra eriophylla | MN755770.1 | - |
Calliandra haematocephala | MN755769.1 | JX870694.1 |
Cojoba arborea | MW849552.1 | JX870758.1 |
Cojoba graciliflora | MW849557.1 | MZ015531.1 |
Faidherbia albida | EF638163.1 | JF270778.1 |
Hesperalbizia occidentalis | MN755774.1 | MW699959.1 |
Lysiloma divaricatum | MN755783 | MN755826 |
Lysiloma latisiliquum | MN755785 | MN755827 |
Mariosousa dolichostachya | EF638084.1 | EF638199.1 |
Vachellia farnesiana | EF638128.1 | EF638219.1 |
Zapoteca formosa | MN755771 | AY125854.1 |
Zapoteca tehuana | MZ327390 A. Campos 4108 (MEXU) | OM634641 A. Campos 4108 (MEXU) |
Ingroup | ||
Ebenopsis confinis | MZ327411 A.L. Reina 696 (FCME) | KF921650.1 |
Ebenopsis ebano | MZ327410 W. Torres et al. 84 (CICY) | EF638101.1 |
Havardia albicans | MZ327403 Duno 1945 (CICY) | OM634648 Duno 1945 (CICY) |
Havardia campylacantha (Gretheria campylacantha) | MZ327405 E. Soto Núñez et al. 8036 (FCME) | OM634650 E. Soto Núñez et al. 8036 (FCME) |
Havardia mexicana | MZ327397 T. R. van Devender 2005-1085 (MEXU) | JX870762.1 |
Havardia pallens | KF921656.1 | EF638194.1 |
Havardia sonorae (Gretheria sonorae) | MZ327404 A. Flores 4875 (FCME) | OM634649 A. Flores 4875 (FCME) |
Painteria elachistophylla | MZ327409 García y Lorence 708 (FCME) | - |
Painteria leptophylla (Ricoa leptophylla) | MZ327407 R. Cruz Durán 224 (MEXU) | OM634651 R. Cruz Durán 224 (MEXU) |
Painteria leptophylla 2 (Ricoa leptophylla) | MZ327406 J. Calónico 3751 (FCME) | C.E. Hughes 1539 (FCME) |
Painteria revoluta | MZ327408 E. López 1107 (CICY) | - |
Pithecellobium diversifolium | MZ327399 A. Laurenio 71 (MO) | JX870768.1 |
Pithecellobium excelsum | MZ327400 Tropical house Bot. Garden Aarhus 2013 | EF638208.1 |
Pithecellobium dulce | OM674458 E. López 1146 (CICY) | MZ015540.1 |
Pithecellobium keyense | MZ327394 Duno et al. 2216 (CICY) | OM634645 Duno et al. 2216 (CICY) |
Pithecellobium lanceolatum | MZ327398 E. Endañú 1310 (CICY) | - |
Pithecellobium winzerlingii | MZ327393 Duno 2434 (CICY) | OM634644 Duno 2434 (CICY) |
Pithecellobium oblongum | MZ327396 I. Coronado & R.M. Rueda 5064 (MO) | OM634647 I. Coronado & R.M. Rueda 5064 (MO) |
Pithecellobium unguis-cati | MZ327395 H. M. Burdet & M. Burdet 02 (MO) | OM634646 H. M. Burdet & M. Burdet 02 (MO) |
Sphinga acatlensis | MZ327391 E. López 1004 (CICY) | OM634642 E. López & E. Endañu 1020 (CICY) |
Sphinga platyloba | MZ327392 Duno et al. 2471 (CICY) | OM634643 Duno et al. 2471 (CICY) |
Thirty-two sequences were newly generated for this study, while 31 sequences were obtained from GenBank (www.ncbi.nlm.nih.gov/genbank); most of the latter were generated for the studies of
Total genomic DNA was extracted from fresh leaves collected from the living collection in the Roger Orellana Regional Botanical Garden of the Centro de Investigación Científica de Yucatán, A. C., from leaflet tissue collected in the field and dried with silica gel or from herbarium specimens deposited in the following Herbaria: CICY, FCME, MA, MEXU, MO, UCOL and ZEA (acronyms as in
Amplifications were performed in an Applied Biosytems Veriti 96 Well Thermal Cycler (Applied Biosystems, Foster City, USA). Volumes of reagents in PCR reactions (all reactions were brought to final volume by adding ultrapure water) and cycling conditions were as follows for the two DNA regions: 1) ETS: 30 μl of mix containing 3 μl 10X Buffer, 2.5 μl MgCl2, 0.6 μl (~ 10 ng) each of primers, 4 μl Q solution, 1 μl 1.25 mM l-1 dNTP, 0.2 μl (1 U) TAQ polymerase, 2 μl (~ 10 ng) DNA; 94 °C for 3 min + 30 cycles (94 °C for 1 min + 60.5 °C for 1 min + 72 °C for 2 min) + 72 °C for 7 min; primers were 18S-IGS and 26S-IGS (
Assembly and editing of sequences were carried out in BioEdit v.7.0.9 (
Posterior Probabilities of < 0.95 were considered weakly supported, whereas PP of 0.95–1.0 were deemed to be well supported. The convergence of MCMC runs was assessed with Tracer v. 1.7.1 (
The Bayesian analysis of ETS and ITS strongly supported the monophyly of the Pithecellobium clade (clade A in Fig.
The other half of the basal dichotomy in the Pithecellobium clade was strongly supported (clade C, PP = 1.0) and grouped a clade (H, P = 1.0) containing two other species of Havardia (H. campylacantha and H. sonorae) with Painteria and Ebenopsis. Two of the three species of Painteria (P. elachistophylla and P. revoluta) formed a strongly-supported clade (K, PP = 1.0) that was placed as the sister group (clade J, P = 0.1) to Ebenopsis; the exclusion of Painteria leptophylla from this clade rendered Painteria paraphyletic.
Our study shows both agreement and disagreement with well-supported results (PP ≥ 0.95 and/or likelihood or parsimony bootstrap ≥ 80%) of previous (
Our results conflict with those of several studies by placing Pithecellobium as the sister taxon to Sphinga (Fig.
The causes of such conflict are unknown. Unlinked DNA regions used in the different studies may reflect different evolutionary histories, each with the potential to be differently impacted by evolutionary phenomena that cause phylogenetic conflict, such as gene duplication, hybridization and incomplete lineage sorting (
Indeed, our study exhibits considerable agreement with the phylogenetic analysis of morphological data in
In cases of conflict between our molecular results and the morphological analyses of
Other phylogenetic analysis in relation to the Pithecellobium clade sampled 15 species for matK (LPGW 2017) and 11 species for 997 nuclear genes (
Our results further substantiate that three of the five genera of the Pithecellobium clade, Ebenopsis, Pithecellobium and Sphinga, are monophyletic, whereas Havardia and Painteria are not. While there exist multiple taxonomic solutions that would yield a classification consisting of only monophyletic genera (see
There are two other nomenclatural options, which, in our opinion, are less appropriate. The first one would be to include all members of clade C (Fig.
As for Havardia and Painteria, the preferred option retains these generic names for the clades that include the generic type species, H. pallens and P. revoluta, respectively. It thus requires the erection of two new genera: one for the clade comprised of H. sonorae and H. campylacantha, another for the species P. leptophylla. These four genera (the re-defined Havardia s.s. and Painteria s.s. and the proposed new genera) are individually diagnoseable by morphology.
Morphological diversity of the genera of the Pithecellobium clade as circumscribed here. Ebenopsis ebano (Berland.) Barneby & J.W. Grimes A inflorescence B pod. Gretheria campylacantha (L. Rico & M. Sousa) Duno & Torke C bark. Pithecellobium excelsum (Kunth) Mart. D bark. Havardia albicans (Kunth) Britton & Rose E inflorescence. Painteria elachistophylla (A. Gray ex S. Watson) Britton & Rose F pod G seed. Pithecellobium dulce (Roxb.) Benth. H leaves. Pithecellobium winzerlingii Britton & Rose I inflorescence. Pithecellobium keyense Britton J inflorescence. Pithecellobium lanceolatum (Humb. & Bonpl. ex Willd.) Benth. K inflorescence. Pithecellobium unguis-cati (L.) Benth. L pod and seed. Pithecellobium lanceolatum (Humb. & Bonpl. ex Willd.) Benth. M pod and seed. Sphinga acatlensis (Benth.) Barneby & J.W. Grimes N branch, leaves and inflorescences O pod. Sphinga platyloba (Bertero ex DC.) Barneby & J.W. Grimes P leaves and inflorescence. Photos: A, B, I–K, P German Carnevali C, D, N, O Colin E. Hughes E, L Gustavo A. Romero F, G Pedro Najéra Quezada, https://www.naturalista.mx) H Peter Pedersen M Rodrigo Duno.
Havardia, as here circumscribed, can be diagnosed within the complex for having both sylleptical and proleptical shoots, inflorescences arising from long shoots, leaves with one pair of pinnae and flowers with recurved corolla lobes. The new genus that we name Gretheria (containing H. sonorae and H. campylacantha) also has both sylleptical and proleptical shoots and inflorescences arising from long shoots, but the pinnae are distally accrescent and the corolla lobes are erect-ascending.
Painteria as redefined here, could be diagnosed by the combination of the valves of the pod elastically reflexed with age, the leaves with just one pair of pinnae and the corolla lobes erect-ascending, whereas the new monotypic genus Ricoa (comprising P. leptophylla), while also having the valves elastically reflexed with age, has leaves with the pinnae decrescent at each end and the corolla lobes recurved.
In the taxonomic treatment that follows, we provide descriptions (drawing heavily from data in
Morphological comparison between the genera of the Pithecellobium clade as circumscribed here (modified from
Ebenopsis | Gretheria | Havardia | Painteria | Pithecellobium | Ricoa | Sphinga | |
---|---|---|---|---|---|---|---|
Habit | Tree or shrub | Shrub or tree | Tree | Shrub | Tree or shrub | Shrub | Shrub or tree |
Leaflets, size | Microphyllous | Microphyllous | Microphyllous | Microphyllous | Micro- to Macrophyllous | Microphyllous | Macrophyllous |
Branching, pattern | Proleptically | Sylleptically and proleptically | Sylleptically and proleptically | Proleptically | Proleptically | Proleptically | Proleptically |
Extrafloral gland, position | Interpinal | Near midpetiole, | Interpinal but the first below proximal pinna-pair or near midpetiole | Between proximal pinna-pair, rarely between 2 pairs, not on petiole proper | Interpinal | between the first pinnae pair | Near midpetiole, rarely at tip of petiole |
Leaflet, venation | Palmate | Pinnate | Pinnate, weakly pinnate, simple, weakly palmate-pinnate | Palmate or simple weakly developed superficially | Pinnate and usually also reticulate | Weakly developed, nearly simple or 1-branched | Pinnate or subpalmate |
Inflorescence | Capitula or shortly spiciform | Capituliform racemes | Capitula or spiciform | Capitula or shortly spiciform | Capitula or spikes | Capitula | Capitula |
Flower, anthesis | Diurnal | Vespertine | Diurnal | Diurnal | Diurnal | Vespertine | Vespertine |
Corolla, lobes | Erect | Erect | Recurved | Erect | Erect | Recurved | Erect |
Disc (ovary) | Absent | Simple callosities or 5-lobed | Absent, obsolete callosities, rarely lobed disc | Callosities obsolete or absent | Callosities obsolete, rarely developed into a lobed disc | Callosties developed or sometimes subobsolete (staminate flowers) | Developed, clasping the stipe |
Funiculus, shape | Straight (not sigmoid) | dilated, sigmoid | Sigmoid | Straight or sinuous (not sigmoid) | Spongy arilliform | Straight or sinuous (nor sigmoid) | Contorted or sigmoid |
Fruit, shape | massive, compressed, sausage-like | Oblong plano-compressed | Oblong or broad-linear straight, plano-compressed | Compressed but turgid, retrofalcate, falcately or subcircinnately broad-linear | oblong or linear in profile, backwardly recurved or coiled and sometimes also twisted | Falcately or subcircinnately broad-linear | Broad-linear plano-compressed |
Fruit, consistence | Woody | Stiff | Chartaceous or thinly coriaceous | Leathery | Leathery or woody | Stiffly leathery | Papery |
Fruit, septation | Yes | No | No | No | No or incipient | No | No |
Seed | Plumply obese | disciform to orbicular | Lentiform, orbicular or oblong-elliptic | Plumby lentiform | plumply | Compressed but plumb | Lentiform |
1 | Trees or shrubs, generally sarmentous; petiolar gland in the mid-petiole; flower bud flask-shaped, flowers opening at night; androecium up to 9 cm long | Sphinga |
– | Trees or shrubs, erect never sarmentous; petiolar gland at the point of origin of the first (or only) pair of pinnae or in the mid-petiole; flower bud ovoid-pyriform, flowers opening during day; androecium usually less than 3 cm long, very rarely up to 7 cm long | 2 |
2 | Petiolar gland below the first pair of pinnae; fruits flattened, papery and straight | 3 |
– | Petiolar gland between the first pair of pinnae; fruits never flattened, never papery and occasionally straight (then woody or sub-woody) | 4 |
3 | Flowers with calyx 1.0–2.0 mm long, teeth 0.25–1.5 mm long, shallowly campanulate; corolla lobes recurved in anthesis; ovary disc absent | Havardia |
– | Flowers with calyx 2.8–3.4 mm long, teeth 0.3–0.8 mm long, deeply campanulate; corolla lobes erect in anthesis; ovary disc present (sometimes poorly developed) | Gretheria |
4 | Leaves with one pair of pinnae and leaflets one pair per pinna or leaves with more than two pairs of pinnae and leaflets two to many pairs per pinna; seeds with fleshy, often brightly coloured arils | Pithecellobium |
– | Leaves with two or more pairs of pinnae, never one, leaflets 2–30 pairs per pinna; seeds without aril | 5 |
5 | Pod cylindrical, woody, straight or slightly curved, deeply internally septate; seeds globose; growing in lowlands of Mexico and the United States (Texas) | Ebenopsis |
– | Pod flattened or slightly subterete, sub-woody and curved, without internal septa; seeds lentiform; growing in highlands of Mexico | 6 |
6 | Leaves with one or two pairs of pinnae; leaflets 3 to 10 per pinna, rarely 12; blades suborbicular, broadly oblong or elliptic (then revolute); corolla lobes ascending | Painteria |
– | Leaves with 3–7(9) pairs of pinnae; leaflets 10 to 25 per pinna; blades narrowly oblong, linear-oblong or lanceolate; corolla lobes recurved | Ricoa |
Similar to Havardia in arboreal or shrubby habit, vegetative branches arising both proleptically and sylleptically, leaves microphyllous, inflorescence arising on long shoots, pod flattened-compressed and seed plumply disciform to orbicular, but differing in the pinnae distally accrescent (vs. decrescent at each end in Havardia), the calyx longer and deeply campanulate (vs. shorter, and shallowly campanulate), and the corolla lobes erect-ascending at anthesis (vs. recurved).
Gretheria sonorae (S. Watson) Duno & Torke.
Xerophytic, microphyllous arborescent shrubs and small trees, 2–14 m tall, commonly armed with stout recurved, lignescent stipules on the trunk and at each node of long-shoots, indumented with minute whitish trichomes on new growth. Leaves bipinnate, with 1–6 (13) pairs of pinnae; leaflets 10–31 per pinna; principal leaf axis typically 2–15 cm long, with the petiole 2–24 mm long, bearing a nectary at or below the mid-point of the petiole, the nectary sessile, shallow-cupular, thick-rimmed or plane and dimpled, pinnae axes sometimes with similar but smaller nectaries between 1–2 (3) distal-most pinna pairs and a minute one at the tip of some pinna-rachises; leaflets opposite, the blade oblong-elliptic to linear-oblong, subcordate at base, obtuse or shortly apiculate at apex; pilosulous or glabrous and marginally ciliolate; venation pinnate, immersed above, prominulous beneath, the mid-rib slightly displaced, giving rise on each side to 2–5 weak secondary veins expiring submarginally or faintly brochidodromous. Inflorescence capituliform racemes arising from leaf axils of long shoots and coeval with or preceding the leaf and/or arising from brachyblasts; peduncles (1.3) 2 cm long; capitula 10–37-flowered, receptacle clavate, 1.5–2.5 mm diameter; bracts ovate, minute, less than 1 mm long, sessile, persistent into anthesis. Flowers sessile, homomorphic, the perianth 5-merous; calyx deeply campanulate, glabrous, teeth deltate-ovate, ciliolate and sometimes distally puberulent or strigose; corolla subcylindrical, lobes erect, white-silky strigose dorsally; androecium 40–52-merous, 9–13 mm long, tube 3.6–5 mm long, nectar disc simple callosities or 5-lobed, 0.2 – 0.35 mm tall; ovary subsessile, slenderly ellipsoid, stipe 0.1–0.25 mm long; style about as long as stamens, the stigma poriform. Pods 1–3 per capitulum, oblong in profile, contracted at base into a pseudostipe ± 5–14 mm long and abruptly so at apex into an erect cusp 1.5–8 mm long; body straight or almost straight, 6.5–13 × (1.3) 1.2–2.4 (2.6) cm, plano-compressed, the valves bluntly framed by longitudinally 3-ridged sutures ±1.5–2 mm wide, stiff, somewhat brittle, brownish-green, externally veinless, glabrous, red-granular or both granular and puberulent outside, the cavity continuous; funicle dilated, sigmoid. Seeds transverse, 8–13, plumply disciform to orbicular in outline, 9–12 × 7–10 mm, the pleurogram U-shaped.
Gretheria comprises two species in United States (Texas), Mexico and Central America (Honduras and Nicaragua).
Gretheria grows in tropical deciduous dry forests, thorn scrubs and brush-woodlands, between sea level and 400 m elevation, occasionally ascending to 700 m.
The generic name honours Rosaura Grether González, an extraordinary and prolific Mexican botanist, with whom we had the pleasure of sharing her experience as a botanist and colleague. Her profound dedication and perseverant commitment to botanical research over decades has contributed importantly to our knowledge and understanding of Leguminosae, especially of the genus Mimosa L.
1 | Petiole 8–24 mm long; leaves with (5) 6–11 (13) pairs of pinnae, leaflets (17) 19–31 per pinna; leaflets linear or linear-oblong, 3.3–6.5 × 0.8–2 mm; capitula 12–37-flowered | Gretheria campylacantha |
– | Petiole 2–7.5 mm long; leaves with 1–5 pairs of pinnae, leaflets (10) 13–21 per pinna; leaflets narrowly oblong or oblong-elliptic, 2.2–5.5 × 0.8–1.3 mm; capitula 10–17-flowered | Gretheria sonorae |
Pithecellobium campylacanthum L. Rico & M. Sousa (as “campylacanthus”), Ann. Missouri Bot. Gard. 73: 722–724. 1986[1987]. Havardia campylacantha (L. Rico & M. Sousa) Barneby & J.M. Grimes (as “campylacanthus”), Mem. New York Bot. Gard. 74(1): 167. 1996.
México. Oaxaca, distrito de Tehuantepec, 7 km al O-NO de Tehuantepec, 17 March 1981, M. Sousa et al. 11938 (holotype: MEXU! 410015; isotypes: BM, CAS accession 0004063 [image!], F accession 2064374 [image!], MEXU accessions 41011 [image!], 410013 [image!], 410016 [image!], MO accession 3481860 [!]).
Gretheria campylacantha occurs discontinuously in the Pacific lowlands of south-eastern Mexico (Guerrero, Michoacán and Oaxaca) and in the interior and Pacific lowlands of Central America (from Comayagua Department in Honduras to Boaco Department in Nicaragua).
It grows in tropical deciduous brush-woodlands, along intermittent streams, between sea level and 200 m elevation, occasionally ascending to 700 m.
Pithecellobium sonorae S. Watson, Proc. Amer. Acad. Arts 24: 49. 1889. Havardia sonorae (S. Watson) Britton & Rose, N. Amer. Fl. 23: 42. 1928.
México. Sonora, common at Guaymas 1887, E. Palmer 58 (holotype: GH accession 00064044 [image!]; isotypes: K accession 000082458 [image!], NDG 46766 [image!], NY accessions 00329628, 00329629 [images!], UC accession 84451 [image!], US accessions 00918587, 00918589 [image!], YU accession 001418 [image!]).
Coastal plain of Baja California Sur, Sonora and Sinaloa in Mexico.
Plains and foothills below 400 m in deciduous dry forest and thorn scrub and along washes in mesquite grassland along the coastal plain.
Ricoa leptophylla (DC.) Duno & Torke.
Similar to Painteria in shrubby habit with pronounced growth dimorphism into long- and short-shoots, deciduous microphyllous leaves and recurved pods with the fruit valves coriaceous to lignescent and elastically reflexed with age, but differing in the leaves with 3–7(9) pairs of pinnae (vs. 1–2 in Painteria), the leaflets 10–25 per pinna (vs. 3–12), the floral bracts 0.8–2.1 mm long (vs. 0.4–0.7 mm), the flowers shortly pedicellate (vs. sessile) and the corolla lobes recurved (vs. erect-ascending).
Low xerophytic stiffly branched microphyllous shrubs 2–1.5 m tall, often growing in patches several metres in diameter, armed at each node of flexuous long shots with a pair of lignescent stipules, young growth indumented with minute whitish hairs. Stipules converted with straight to recurved spines with a thickened base, the spines 3–10 mm long. Leaves bipinnate with 3–7 (9) pairs of pinnae; leaflets 8–25 pairs per pinna, the primary leaf axis 0.5–5 cm long, with the petiole 2.5–10 (18) mm long and a subsessile circular nectary between the first pinnae pair (sometimes also between the second pair), nectaries absent on pinna-rachises; leaflets opposite, narrowly- or linear-oblong or lanceolate, semi-cordate at base, obtuse to weakly apiculate at apex, puberulous abaxially, marginally ciliate, the venation weakly developed, nearly simple or 1-branched, the mid-rib prominulous only dorsally, subcentric. Inflorescence of capitula arising from brachyblasts, peduncle 1–18 mm long; receptable clavate, 1.5–2.5 mm long, capitula globose, 1–1.5 cm in diameter, 16–35-flowered; bracts linear-oblanceolate or spatulate, 0.8–2.1 mm long, persistent into anthesis. Flowers externally homomorphic, but some functionally staminate, pedicellate, perianth 5-merous; pedicel 0.2–0.6 mm long; calyx campanulate, contracted at base, 1.3–3.2 mm long, minutely puberulent (or just on teeth), teeth ovate or deltate, 0.2–0.9 mm long; corolla reddish or greenish, tubular, 3.5–5 mm long, lobes ovate, recurving. 1.2–1.9 mm long, puberulous and densely fimbriolate on lobes; androecium 40–76-merous, 5–10.5 mm long, tube 2–4 mm long; ovary slenderly ellipsoid, compressed, glabrous, on a short stipe 1–1.4 mm long, style in bisexual flowers often longer and more robust than stamens. Pods l–2 (4) per capitulum, falcately or subcircinnately broadly linear in profile, attenuate into an erect cusp 2–6 mm long, the body 7–11.5 × 1.1–1.9 cm, 8–10-seeded, the valves stiffly leathery, at first plano-compressed, becoming turgid and low-convex (on both faces of pod) over each seed, densely grey puberulent, becoming glabrescent and dark castaneous, indistinctly venulose, the cavity continuous, dehiscence inert through both sutures; funicle straight or sinuous (but not sigmoid), seeds obliquely descending, 8–10, plumply lentiform, 7.5–11 × 3–4 mm, the testa smooth, hard, moderately lustrous, dark castaneous, the pleurogram incomplete.
Ricoa is found scattered over the Mexican Central Plane, in the States of Chihuahua, Coahuila, Durango, Guanajuato, Hidalgo, Jalisco, México, Michoacán, Oaxaca, Puebla, Querétaro, San Luis Potosí, Tlaxcala and Zacatecas.
It grows in grasslands, scrubs and at the lower edge of the pine-oak belt, on both basaltic and calcareous substrates, at 1600–2800 m elev. Plants flower between March and August.
The common name is Huisache. This name is also given to Vachellia farnesiana (L.) Wight & Arn. and other related species (
The generic name honours María Lourdes Rico, whose profound dedication and perseverant commitment to botanical research over decades has deeply enhanced knowledge and understanding of the Leguminosae, especially tribe Ingeae.
Acacia leptophylla DC., Cat. PI. Horti Monsp. 74. 1813. Mimosa leptophilla [sic] Cavanilles, Elench. PI. Horti Matr. 24. 1803, nom. nud. Pithecellobium leptophyllum (DC.) Daveau, Bull. Soc. Bot. France 59: 635, t. XVI. 1912. Painteria leptophylla (DC.) Britton & Rose, N. Amer. Fl. 23: 36. 1928.
Mexico. verosimiliter in Hispanorum territorio Americano, P. M. A. Broussonet s.n. [870]. (holotype: M; isotypes: G-DEL [image!], photo, MO [image!]).
We thank National Council of Science and Technology (CONACYT), for the financial support through the project 81799 and the Centro de Investigación Científica de Yucatán A.C. (CICY). All molecular work was done in the Laboratory of Molecular Markers (Unidad de Recursos Naturales). We remain especially grateful to Dr. Miriam Monforte and biologists Matilde Margarita Ortiz García, Verónica Limones Briones, Nestor Raigoza and Silvia Hernández. We would like to thank the curators of the Herbaria (CIQR, ENCB, FCME, GH, MA, MEXU, MA, MO, NY, GUADA, UADY, UAMIZ, UCAM and US) whose material of Pithecellobium clade we borrowed and/or studied. The last author would like to acknowledge an A. Gentry scholarship that allowed him to study plant material at MO, including material of the tribe Ingeae. We thank two anonymous reviewers whose suggestions helped improve and clarify this manuscript.