Research Article |
Corresponding author: Helga Ochoterena ( helga@ib.unam.mx ) Academic editor: João Farminhão
© 2023 Alejandro Torres-Montúfar, Hilda Flores-Olvera, Heriberto Ávila-González, Arturo Castro-Castro, Helga Ochoterena.
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:
Torres-Montúfar A, Flores-Olvera H, Ávila-González H, Castro-Castro A, Ochoterena H (2023) An assessment of Coutaportla (Chiococceae, Rubiaceae) with the description of a new species from Mexico. Plant Ecology and Evolution 156(1): 3-12. https://doi.org/10.5091/plecevo.89764
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Background and aims – Ongoing studies on Mexican Rubiaceae revealed an undescribed species of Coutaportla endemic to the Sierra Madre Occidental pine-oak forests in the state of Sinaloa, near the border with Durango, Mexico. The species is here described and illustrated, and its morphological characters are compared with those of the other species in the genus.
Material and methods – This study is based on field observations, examination of herbarium specimens including digital images, and morphological studies based on samples from dried and spirit specimens.
Key results – The morphological comparison of taxonomically important characters among the species of Coutaportla reveals conditions that were previously not reported for the genus. The placentation and ovule number of C. lorenceana, which belongs in the Portlandia complex, is comparable to that in the Chiococceae tribe. This tribe was proposed to include the latter complex based on molecular data, but the classification was controversial according to the morphology. Coutaportla lorenceana hence provides a morphological link between the Portlandia complex and the taxa traditionally placed in Chiococceae. The new species is assessed as Critically Endangered following the IUCN Red List criteria.
Mexican flora, Neotropics, pine-oak forest, placentation, Santuario El Palmito, Sierra Madre Occidental, taxonomy
The monophyly of the tribe Chiococceae, within the Cinchonoideae subfamily (Rubiaceae), including the tribe Catesbaeeae and the genera previously grouped in the Portlandia complex (
The tribe Chiococceae includes erect or scandent subshrubs, vines, treelets, and tall trees; flowers with four to eight parts; corolla tubes ranging from few millimetres in length (e.g. Erithalis P.Browne) to 27 cm (e.g. Osa Aiello); cylindrical or flattened, dry (capsular) or fleshy (drupes or baccate) fruits; and flat, polygonal, or globose winged or wingless seeds. Chiococceae has an amphi-Pacific tropical distribution, but its species are primarily distributed in the Neotropics, with centres of diversity in the Caribbean islands (16 endemic genera and ca 160 spp.), Mexico and Central America (two endemic genera: Coutaportla Urb. and Nernstia Urb.), South America (four endemic genera: Adolphoduckea Paudyal & Delprete, Coutareopsis Paudyal & Delprete, Motleyothamnus Paudyal & Delprete, and Salzmannia DC.), and the islands of the western Pacific Ocean (one endemic genus: Thiollierea Montrouz.) (
Coutaportla is a Madrean/Mesoamerican genus that can be morphologically distinguished from other Chiococceae genera by the combination of 4(–5)-merous flowers, variable ovule attachment position, and capsular fruits with few (2 to 5) seeds, in contrast to the other genera in the tribe that have 5–8-merous flowers, and, few or numerous ovules per locule, basal, medial, or apical placentation, and either capsular or fleshy fruits (
Coutaportla was described by Urban in 1923 based on Portlandia ghiesbreghtiana Baill. due to its peculiar placentation and floral morphology. It was a monotypic genus until Portlandia guatemalensis (Standl.) Lorence was transferred to this genus by
During the course of a systematic study of Coutaportla, we found fruiting treelets in the temperate forest of the Sierra Madre Occidental, in Sinaloa state, near the border with Durango state, Mexico, that were first doubtfully assigned to Chiococca P.Browne due to the flattened, few-seeded fruits with apical placentation, with the immature fruits being rather chartaceous, not fleshy as in Chiococca. At the end of summer 2019, we visited the locality again and found these treelets in bloom, which made us realise that they correspond to a species of Coutaportla, morphologically similar to C. ghiesbreghtiana, but with significant differences that allow us to propose it as a new species. In this paper, we describe and illustrate this novelty and present an updated treatment of Coutaportla, including a revised key to its species.
The authors collected specimens between 2017 and 2019 at Santuario El Palmito natural protected area (
The distribution maps were drawn using locality data from all consulted herbarium specimens using QGIS Desktop v.3.4.11 (QGIS Development Team 2021). The maps were prepared using cartography shapefiles acquired from
Lorencea
(
Coutaportla ghiesbreghtiana (Baill.) Urb.
Shrubs, treelets, or trees. Stipules triangular to deltoid, persistent, intrapetiolar, adpressed. Leaves opposite, petiolate. Inflorescence terminal or axillar, bracteate, racemose, cymose, or solitary flowers. Flowers hermaphrodite, 4-merous, rarely 5-merous, pedicellate, homostylous, fragrant; corolla infundibuliform, white, pink, or lavender, with imbricate aestivation; stamens with filaments basally inserted to the corolla and connate, anthers basifixed; stigma slightly bilobed; ovary 2-locular, with 1–5 ovules per locule, placentas basal, central, or apical. Fruits capsular, clearly woody at maturity, ellipsoid to oblate, strongly compressed, perpendicular to the septum, with persistent calyx lobes; dehiscence at first loculicidal, then septicidal. Seeds vertically attached to the placenta, flattened, wingless, with thickened margins.
1 | Leaves orbicular, less than 1.2 cm long, mucronate at apex; corolla pink | C. pailensis |
– | Leaves elliptic to lanceolate-/obovate-/ovate-elliptic, more than 1.3 cm long, acuminate or apiculate at apex; corolla white or lavender | 2 |
2 | Corolla lavender; ovary with apical placentas; capsules with one seed per locule | C. lorenceana |
– | Corolla white; ovary with basal or central placentas; capsules with 4–5 seeds per locule | 3 |
3 | Shrubs or treelets; leaves with 4–5 pairs of secondary veins on each side of midrib; corolla 4-merous; seeds 4–5 mm long; plants growing in xerophytic (scrubs) and dry forests | C. ghiesbreghtiana |
– | Trees; leaves with 7–10 pairs of secondary veins on each side of midrib; corolla 5-merous (rarely 4-merous); seeds 6–8 mm long; plants growing in rainforests | C. guatemalensis |
Chiococca grandiflora
Lorence & T.Van Devender, pro parte (
MEXICO • Sinaloa, Municipio: Concordia. El Palmito, alrededores del acceso principal al Santuario Chara Pinta; 23.56444°N, 105.848882°W; 1980 m; 10 Sep. 2019; fl.; Castro-Castro, Ávila-González. & Zavala-Pérez 4532; holotype: MEXU; isotype: CIIDIR, FCME, FESC, IEB, IBUG, MO, PTBG, SLPM.
Coutaportla lorenceana differs from all the other species in the genus by the lavender corollas, the apical ovule placentation, and the capsules with 1-seeded locules. It most closely resembles C. ghiesbreghtiana (Baill.) Urb. by the treelet habit and leaf size and shape, but it differs by the leaves acuminate at the apex (vs apiculate in C. ghiesbreghtiana), the chartaceous leaf blades (vs subcoriaceous in C. ghiesbreghtiana), the 3–9-flowered inflorescences (vs solitary flowers in C. ghiesbreghtiana), and the lavender corollas (vs white in C. ghiesbreghtiana).
Treelets 2–4 m tall. Twigs glabrous, greenish-brown, terete, striated; apical twigs resinous. Stipules rigid, broadly deltoid, 1.8–2.3 × 2–3.8 mm, acuminate at apex, basally connate, externally glabrous, internally with resinous colleters. Leaves petiolate, those of the same pair equal to subequal; petioles glabrous, 8–17 mm long, adaxially flat, distally winged; blades elliptic to elliptic-lanceolate, 1.3–5.8 × 0.8–1.4 cm, attenuate at base, acuminate at apex (acumen up to 1 cm long), chartaceous, matte and glabrous on both sides, concolorous; venation brochidodromous, 4–6 pairs of secondary veins on each side of midrib; domatia absent. Inflorescence axillary or rarely terminal on lateral branches, cymose, 3–9 flowered, 2.3–3.5 cm long (including the corollas); peduncles 0.2–1.4 cm long; bracts triangular, 1.3 × 0.5 mm. Flowers 4(–5)-merous; pedicels 1–4 mm long; hypanthium obconical, laterally flattened, 1–2 mm long. Calyx tube 0.4 mm long, lobes equal, subulate, rigid, erect, 1–1.5 × 0.3–0.4 mm, colleters absent. Corolla infundibuliform, lavender, tube 1.7–2.5 cm long, 0.7–0.9 cm wide at mouth, externally and internally glabrous; lobes narrowly imbricate in bud, triangular. Stamens 1.8–2.7 cm long; filaments puberulent; anthers linear. Style 2.3–2.8 cm long, glabrate. Ovules apically inserted. Capsule oblate, 4–5 × 4–5 mm. Seeds one per locule, thin, discoid, 3 × 1.2 mm, brown; testa granulate.
Coutaportla lorenceana. A. Flowering branch. B. Detail of the venation on the abaxial leaf surface. C. Stipule and immature fruiting branch. D. Inflorescence. E. Flower. F. Ovary and calyx longitudinally dissected. G. Dissected corolla. H. Androecium. I. Detail of the puberulent filaments. J. Style. K. Capsule longitudinally dissected showing seed attachment. L. Seed. Drawn by Albino Luna (A–J, from A. Castro-Castro et al. 4532; K–L from A. Castro-Castro et al. 4695).
Coutaportla lorenceana. A. Habit. B. Twigs showing intrapetiolar persistent stipules. C. Flowering branch. D. Inflorescences showing corolla shape and colour. E. Longitudinal section of the ovary showing apical placentation in lateral (perpendicular to the fruit compression plane) and frontal (parallel to the fruit compression plane) views. F. Immature fruits. Photographs by Arturo Castro-Castro (A–D, F) and Helga Ochoterena (E).
Endemic to Mexico. Only known from the oak-pine forest in El Palmito, Sinaloa state, on rocky slopes, in the Tropical Madrean Region (
Flowering in September and fruiting in October and November.
The specific epithet is dedicated to David Lorence, who has immensely contributed to the knowledge of Mexican Rubiaceae, establishing for the first time an enviable collection for the family at MEXU, which serves as an invaluable basis for research.
The species is given a Red List status of Critically Endangered [CR B1a+b(iii); B2a+b(iii)]. Coutaportla lorenceana is known from three collections, representing three occurrences, at relative proximity around El Palmito in Mexico. The extent of occurrence (EOO) is of 0.76 km2 and the area of occupancy (AOO) is of 8 km2. Both EOO and AOO fall within the limits of the Critically Endangered (CR) category under subcriteria B1 and B2. Since this species occurs at a single location and is threatened by logging and agricultural encroachment, it meets the conditions for the CR category.
MEXICO • Sinaloa: Municipio: Concordia, El Palmito, km 201 de la Carretera Durango-Mazatlán; 23.566917°N, 105.84525°W; 1966 m; 6 Nov. 2020; fr.; Castro-Castro, Ávila-González & González-Gallegos 4695; CIIDIR, FCME, FESC, MEXU • Ca 2 km al N de El Palmito; 1955 m; 24 Oct. 2017; fr.; Torres-Montúfar, Morales-García & Castro-Castro 987; ENCB, FESC, MO, PTBG.
Coutaportla lorenceana has distinctive features that firmly support its recognition as a new species. Although it is substantially different from the other species in the genus, there is no doubt about its assignment to Coutaportla, despite the lack of molecular phylogenetic evidence, considering the mainly 4-merous flowers and the flattened capsular fruit. There are several morphological features, besides the type of habitat, that distinguish the species within Coutaportla (Table
Comparison of morphological characters and habitat of Coutaportla species.
Character | C. lorenceana | C. ghiesbreghtiana | C. guatemalensis | C. pailensis |
Habit | Treelet | Shrub or treelet | Tree | Shrub |
Leaf blade shape | Elliptic to elliptic-lanceolate | Elliptic to ovate-elliptic | Elliptic to obovate-elliptic | Orbicular |
Leaf length | 1.3–5.8 cm | 1.7–4.5 cm | 11–22 cm | 0.4–1.2 cm |
Leaf apex | Acuminate | Apiculate | Acuminate | Mucronate |
Number of secondary veins on each side of midrib | 4–6 | 4–5 | 7–10 | Indistinct |
Inflorescence position | Axillary and terminal | Axillary | Axillary and terminal | Terminal |
Flower merosity | 4(5) | 4 | 5(4) | 4(5) |
Calyx colleters | Absent | Present | Absent | Present |
Corolla colour | Lavender | White | White | Pink |
Corolla length | 1.7–2.5 cm | 2–2.5 cm | 2.5–3.5 cm | 2–3.8 cm |
Placental position | Apical | Central | Basal | Central |
Capsule size | 4–5 × 4–5 mm | 7–10 × 6–7 mm | 10–14 × 12–16 mm | 8–10 × 4–5 mm |
Number of seeds per locule | 1 | 4–5 | 4–5 | 2–5 |
Seed length | 3 mm | 4–5 mm | 6–8 mm | 3–4 mm |
Habitat and distribution | Pine-oak forest (Mexico: Sinaloa) | Xerophytic scrubland, dry forest (Mexico: Hidalgo, Oaxaca, Puebla) | Rainforest (Honduras; Guatemala; Mexico: Chiapas, Veracruz) | Xerophytic scrubland, (Mexico: Coahuila) |
Longitudinal ovary sections (left column) and diagrams (right column), comparing the seed attachment and placenta shape and position within the locule (grey coloured area in the diagrams) in Coutaportla. Placenta position is indicated by a black arrow on the photographs. Scale bars correspond to 1 cm. A–B. Central: C. ghiesbreghtiana, A from Aguilar et al. 4 (MEXU). C–D. Basal: C. guatemalensis, C from Stevens et al. 25474 (MEXU). E–F. Central: C. pailensis, E from Villarreal et al. 3063 (MEXU). G–H. Apical: C. lorenceana sp. nov., G from Torres-Montúfar et al. 987 (MEXU).
The apical placentation of the new species completes a range in the ovule attachment in Coutaportla from the base to the top, raising further questions regarding the acceptance of Lorencea as a distinct genus. The monotypic genus Lorencea was described primarily based on the tree habit (vs treelet or shrub in Coutaportla), the 5-merous (rarely 4-merous) flowers (vs mainly 4-merous flowers in Coutaportla), and the basal placenta attachment (vs central placenta position in Coutaportla) (
Due to the overlap of many characters among the species of Coutaportla and Lorencea, as well as the fact that both genera are sister, we prefer to recognise only Coutaportla (including Lorencea), as in the Rubiaceae treatment of the Flora Mesoamericana (
The placenta is present at various positions among the different species of Coutaportla, and it is possible to associate this variation with the differences in fruit compression and size. Among the species in the genus, there is variation in fruit and seed sizes as well as seed number, ranging from many-seeded relatively large fruits with relatively large seeds basally attached, to relatively many-seeded medium size fruits with smaller seeds centrally attached, to relatively small fruits with one smaller seed apically attached. Aside from the new species here described, none of the taxa in the Portlandia complex formerly excluded from Chiococceae have apical placentation, which justifies the initial scepticism regarding the molecular phylogenetic results and the placement of this generic complex within that tribe. The new species shows a placentation similar to that of the species with fleshy fruits classified in Chiococceae, in its previous restricted sense. The less inclusive most recent common ancestor of Chiococceae sensu stricto in the phylogenetic tree (
Such highly variable placentation is likewise present among genera in the rest of Chiococceae, namely in Chiococca and Erithalis in which it is apical, in Hintonia and Portlandia in which it is central, while C. guatemalensis is the only taxon with basal placentation. This is in contrast to most other higher taxa of the Rubiaceae, where an either basal or apical placentation is characteristic for many tribes, e.g. apical in Vanguerieae and basal in Psychotrieae. However, some anatomical and development studies have shown that placentation can also be extremely variable in Rubiaceae (
The discovery of the species Coutaportla lorenceana sheds a new light on character evolution of the Chiococceae sensu lato. We hope that describing this narrowly endemic species from the Sierra Madre Occidental will further help the conservation efforts in the area, demonstrating how floristic studies in Mexico are still highly needed and to be encouraged. Additionally, the discovery of a species in a genus that has species with restricted geographic distribution and present in different vegetation types in Mexico opens biogeographic questions related to ecosystem adaptations and character evolution.
We wish to thank Albino Luna for preparing the detailed and extraordinary line drawing. We also thank Fernando Valdez for providing accommodation and Santos Vázquez for guiding and supporting us during the botanical explorations. We are grateful to Elmar Robbrecht, João Farminhão, and another anonymous reviewer for their very relevant comments. This research was partially supported by the Programa de Apoyo a Proyectos de Investigación e Innovación Tecnológica (PAPIIT, research project IA204021), Programa Institucional de Formación de Investigadores (PIFI), and Floristic Inventory Project in La Chara Pinta Sinaloa Reserve (SIP 20180521) from Instituto Politécnico Nacional, and a Madrean Discovery Expeditions Scholarship for H.A.G.