Sideroxylon cochranei A.Vázquez & Santana Mich., 2021

Vázquez-García, J. Antonio, Santana-Michel, Francisco J., Cuevas-Guzmán, Ramón & Ortega-Peña, A. Salomé, 2021, Sideroxylon cochranei (Sapotoideae, Sapotaceae): a new cloud forest tree species from the Sierra de Manantlán and Cuale in western México, Phytotaxa 498 (2), pp. 113-122 : 116-120

Sideroxylon cochranei A.Vázquez & Santana Mich. , sp. nov. ( Figs. 2–3 )

Type: — MEXICO. Jalisco: Municipio de Tolimán , 3 km al oeste de El Terrero, bosque mesófilo de montaña, 2300 m, 19 November 1993 (fl), F . J . Santana-M. & B. F . Benz 6705 (holotype: ZEA!)

Diagnosis:— Sideroxylon cochranei is morphologically close to the geographically distant S. salicifolium , but it differs from the latter in being a highland cloud forest tree growing from (1500–) 1900 to 2300 m asl vs. a lowland to lower montane tropical tree growing from 10 to 1500 m asl; also in having leaves not clustered vs. clustered with longer petioles 2.0–3.5 vs. 0.5–1.2 cm long; longer sepals (3.0–)4.0–5.0 vs. (1.5–)2.0– 2.5 mm; and larger fruits 1.0–1.3 vs. 0.6–0.8 cm in diam. ( Table 1).

Evergreen trees, unarmed (4.5–)10.0–25.0 m tall, 40 cm dbh; bark grey smooth and finely fissured. Branches ascending, from 2.0–7.0 m above the ground; leaves (6.0–)7.0–11.0(–2.0) × 2.0–3.0 cm wide, entire, lanceolate, glabrous, apex acute to acuminate, base attenuate, with pinnately parallel nerves; petioles 2.0– 3.5 cm long, spirally arranged and clustered toward the apex. Flowers arranged in fascicles at the branch nodes; fascicles 0.7–1.0 cm in diam., finely pubescent, ferrugineous, pedicels (1.7–)2.0–3.0(–3.5) mm long, flowers radiate, (3.5–)4.0–7.0 mm in diam.; sepals 5, rounded, appressed pubescent, ferrugineous, (3.0–)4.0–5.0 mm long; corolla green-yellowish 2.0–3.0 mm long; 5-lobed, lobes five, median segment elliptic, with rounded apex, lateral segments narrowly acute, about 1.0 mm long; stamens 5(–6), terete, staminodes 5(–6), petaloid, lanceolate, margin erose, shorter than the lobes; ovary superior, glabrous, ovules 5; style 1.5–2.5 mm long. Fruit globose, 1.0– 1.3 cm diam.; peduncle 4.0–6.0 mm long. Seeds 2, rarely 1, scar ventral, 8.0–9.0 mm long, 5.0–6.0 mm wide, brown.

Distribution and Habitat:—It is known only from Sierra de Manantlán and Sierra de Cuale, in south-western Jalisco state, western Mexico. It has been recorded as abundant in Cerro Grande, the type locality (Vázquez-García 1995). It grows in cloud forest and pine-oak forest coexisting with Clethra fragrans L.M. González & R. Ramírez , Cornus excelsa Kunth , Dendropanax arboreus (L.) Decne. & Planch., Fraxinus uhdei (Wenz.) Lingelsh. , Garrya laurifolia Hartw. ex Benth. , Ilex tolucana Hemsl. , Litsea glaucescens Kunth , Lobelia laxiflora Kunth , Montanoa andersonii McVaugh , Myrcianthes fragrans (Sw.) McVaugh , Oreopanax xalapensis (Kunth) Decne. & Planch. , Ostrya virginiana (Mill.) K. Koch , Pinus douglasiana Martínez , P. oocarpa Schiede ex Schltdl. , Quercus calophylla Schltdl. & Cham. , Q. laurina Bonpl. , Q. rugosa Née , Q. scytophylla Liebm. , Styrax argenteus C. Presl , Symplocos citrea Lex. ex La Llave & Lex. , Ternstroemia lineata DC. , Tilia caroliniana Mill. subsp. occidentalis (Rose) Pigott , Xylosma flexuosa (Kunth) Hemsl. , and Zinowiewia concinna Lundell.

Phenology:—Flowering from October to December and from April to May; fruiting from February to March and from May to October.

Etymology:—This taxon honors Theodore S. Cochrane, for his great contribution to the knowledge of the Flora of Manantlán, and in gratitude to his support during systematic vegetation surveys along an altitudinal gradient on the Cerro Grande massif (Vázquez-García 1995, Vázquez-García & Givnish 1998), which led to the discovery of this new tree species.

Conservation status:—We assessed Sideroxylon cochranei as critically endangered (CR) and met the following IUCN (2019) criteria: B2, the species occurred in less than 10 km 2; B2a, present only in four populations (localities); and B2b, habitat reduction was inferred, in two of the four localities, from livestock and agricultural expansion, including Agave maximilana , the raicilla beverage. C, less than 250 individuals; C1, endangered, since we estimated a 20% reduction in two generations; and C2a, less than 50 individuals.

Additional specimens examined (paratypes):— MEXICO. Jalisco: Municipio de Autlán , 2 km al S de Zacahuautla, camino a la Estación Científica Las Joyas, 25 November 1991 (fl), J . A . Solís-M. 4938 ( ZEA); 1500–1600 m, 11 October 2003 (fl, fr), R . Cuevas-G., N. M . Núñez-L., F. M . Cuevas-N. & A. M . Cuevas-N. 8435 ( ZEA); Cañada El Fresnal, Sierra de Manantlán , 1500 m, 22 February 2003 (young fr), R . Cuevas-G., E. V . Sánchez-R., G. Guzmán, M . Cuevas-G., A. Cisneros-L. 7694 ( ZEA); Cañada de La Tuna, Estación Científica Las Joyas , 1940 m, 29 October 2015 (st), R . Cuevas-G. & E. J . Jardel P . 11559 ( ZEA). Municipio de Casimiro Castillo , 1.5 km al SW de Corralitos, 1750 m, 13 October 1998 (st), R . Cuevas-G., L. Guzmán-H. & J. Aragón 6146 ( ZEA). Municipio de Cuautitlán , 2.5 km al W de la Estación Científica Las Joyas, Cañada del Laurelito , 1730 m, 5 April 1991 (st), E . J . Jardel-P., A. Santiago & E . Muñoz-M. 238 ( ZEA). Municipio de Talpa de Allende, brecha Talpa-Cuale , 1520 m, 3 May 2003 (fr), F . J . Santana-M., R. Cuevas-G., L. Guzmán-H. & E. V . Sánchez-R. 11384 ( ZEA); Municipio Tolimán : 3 km al NW de El Terrero, Piedras Verdes, 2150 m, 19 May 1991 (st), E . J . Jardel-P., E. Muñoz-M. & A. Santiago 291 ( ZEA); 2 km al NW de El Terrero, 12–13 km al ENE de Minatitlán , 2300 m, 16 March 1993 (st), E . Muñoz-M. & M. Vázquez 47 ( ZEA, WIS); 3 km al NW de El Terrero , 2300 m, 19 November 1993 (fl), F . J . Santana-M. & B. F . Benz 6568 ( ZEA); 3 km al W de El Terrero , 2300 m, 20 May 1994 (fr), F . J . Santana-M. & L. Guzmán-H. 6673 ( ZEA); 15 July 1994 (fr), F . J . Santana-M., B. F . Benz & J . Rosales A . 6705 (ZEA).

Key to the species of Sideroxylon of western Mexico (adapted from Pennington 1990)

1. Corolla lobes entire (without lateral segments)..................................................................................................................................2

- Corolla lobes divided into a median segment and two smaller lateral segments...............................................................................3

2. Petiole 1.0– 2.6 cm long; lower leaf surface pubescent to tomentose; corolla 5–5.5 mm long ......................................... S. tepicense

- Petiole (2.7–)4.0–8.0 cm long, lower leaf surface softly pubescent to glabrous; corolla (5.5) 6–8.5 mm long ..................... S. capiri

3. Plant not spiny, venation eucamptodromous or brochidodromous....................................................................................................4

- Plant spiny, venation brochidodromous.............................................................................................................................................6

4. Venation eucaptodromous; leaf apex often rounded or obtuse sometimes acute to attenuate; corolla 4–6.5 mm long....................... .................................................................................................................................................... S. portoricense subsp. minutiflorum

- Venation brochidodromous; leaf apex attenuate, acute or acuminate; corolla <4 mm long..............................................................5

5. Near sea-shore to lower montane tropical trees growing from 10 to 1500 m asl; petioles 0.5–1.2 cm long; sepals (1.5–)2.0– 2.5 mm long; fruit 0.6–0.8 cm in diam ....................................................................................................................................... S. salicifolium

- Montane cloud forest trees growing from (1500–) 1900 to 2300 m asl; petioles 2.0– 3.5 cm long; sepals (3.0–)4.0–5.0 cm long; fruit 1.0– 1.3 cm in diam ........................................................................................................................................................... S. cochranei

6. Lower leaf surface persistently appressed puberulous with white hairs, leaf margin often undulate, fruit globose............................ ............................................................................................................................................................................................. S. palmeri

- Lower leaf surface not appressed puberulous with white hairs, leaf margin not undulate, fruit narrower, not globose..................................................................................................................................................................................................................................7

7. Lamina infolded along the midrib; tube of the corolla 2–3 mm long; seed narrowly oblong, twice as long as broad ........................ ................................................................................................................................................................................... S. stenospermum

- Lamina not infolded along the midrib; tube of the corolla 1–1.5 mm long; seed broader, less than twice as long as broad...........................................................................................................................................................................................................................8

8. Leaves usually 5–12 cm long, elliptic to oblong-elliptic, less often lanceolate or ovate, with 10–20 pairs of secondary veins, and conspicuous intersecondaries; apex narrowly attenuate, acute or obtuse.......................................................................... S. persimile

- Leaves smaller, not exceeding 8 cm long, elliptic to broadly oblanceolate, secondaries veins 5–9 pairs; apex acute ........................ ................................................................................................................................................................................... S. cartilagineum

Discussion:—In agreement with the GLC of species ( De Queiroz 2007) phenetical and ecological evidence support the species status of Sideroxylon cochranei . This species differs from S. salicifolium in four morphological characters: including unclustered leaves, longer petioles, longer sepals and larger fruits. Additionally, these species are not only geographically distant but the former grows at higher elevations (1500–)1900 to 2300 vs. 10 to 1500 m asl and occurs at montane cloud forest habitat vs. lower montane tropical forest.

Sideroxylon cochranei is morphoplogically close to S. salicifolium , and it is yet to be tested if they belong in the same lineage, tribe Sideroxyleae , Sapotoideae , Clade 2 of Anderberg & Swenson (2003) and within the Sideroxyleae, Neotropical subclade I, of Stride et al. (2014).

Even though that Sideroxylon cochranei and S. portoricense subsp. minutiflorum , have an overlapping elevational niche breadth within the Sierra de Manantlán (1500–2300 vs. 1700–1900) m, they are nonetheless allopatric (the former endemic to Cuale, central and eastern Manantlán vs. the latter from western Manantlán and widely distributed). They also differ considerably in leaf size.

The narrow-leaf syndrome, a functional and evolutionary adaptation to intercept and harvest fog with greater efficiency ( Martorell & Ezcurra 2007), may have allowed S. cochranei to conquer a wider elevational and geological niche breadth including the calacareous eastern Manantlán, where plants are under greater water-stress as there are no streams, since rainfall water quickly seeps to the phreatic mantles through cracks and crevices carved in the rock ( Vázquez-García & Givnish 1998).

Reports of Sideroxylon in Central jalisco, particularly those from the Barranca del Rio Santiago, Jalisco (Sahagún et al. 2014) listed as S. cartilagineum , as well as that of S. persimile ( López-Velázquez et al. 2011) actually correspond to S. persimile subsp. sessiliflorum .

Figures

FIGURE 2. Sideroxylon cochranei. A. Fruiting branch. B. Floriferous branch. C. The entire flower (left) and gynoecium showing the open corolla and staminodes (right). D. Fruit. E. Seed. Illustration by Enrique V. Sánchez R.

FIGURE 3. Sideroxylon cochranei.A. Immature fruits, from El Fresnal. Sierra de Manantlán, Cuevas-G. et al. 7694. B. Mature fruits from Sierra de Cuale, Santana-M. et al. 11384. Photographs by R. Cuevas-G.