Introduction

The neotropical genus Clusia L. comprises 300 – 400 species, making it the largest genus of Clusiaceae in the region. Within Central America, 19 species of Clusia have been preliminarily reported in Panama (Woodson et al. 1980), however, this omits C. cooperi Standl., as well as recently described species such as C. guabalensis Luján & Aranda (Luján et al. 2018), so the number of described Clusia species in Panama is at least 21. In Costa Rica, at least 32 species of Clusia have been reported (Hammel 2010). The taxonomic understanding of Clusia, nevertheless, remains incomplete, with many species remaining either undescribed or poorly documented. This gap can be largely attributed to the dioecy exhibited within the genus, with many species displaying very similar vegetative morphologies. Despite this lack of taxonomic clarity, the genus is well known for displaying a number of unusual characteristics, such as the ability to undergo CAM photosynthesis (Tinoco-Ojanguren & Vázquez-Yanes 1983; Luján et al. 2023) and the production of flower resins as a pollinator reward in some species (Gustafsson & Bittrich 2002). Recent advances in molecular analysis have provided support for Clusia to be identified as a monophyletic group (Gustafsson & Bittrich 2002; Gustafsson et al. 2007; Luján 2019), however, deep evolutionary relationships within the genus remain largely unresolved. Here we provide a description of one recently recognised, new species and discuss its affinities, distribution and conservation status.

Methods

Herbarium specimens were studied at CR, K, MO and USJ (acronyms follow Thiers 2023, continuously updated), using dissecting microscopes and following Beentje’s (2016) terminology to describe morphological characters. The species conservation status was assessed following the IUCN (2022) red list categories, criteria and guidelines, and the GeoCat tool (Bachman et al. 2011) with a cell width of 2 × 2 km was used to estimate extent of occurrence (EOO) and area of occupancy (AOO).

Taxonomic Treatment

Clusia salicifolia Wodcke & Hammel sp. nov. Type: Costa Rica, Turrialba. Along the right hand bank of the Barbilla River, between the San Miguel and Jesús ravines, 400 m, 19 March 1996, G. Herrera, E. Moya & P. Kuss 8812 (♂) (holotype K!, isotypes CR!, MO!).

http://www.ipni.org//urn:lsid:ipni.org:names:77336762-1

Hemiepiphytic tree; dioecious; epidermis non exfoliating; resin colourless. Leaves with petioles 0.9 – 1.7 cm, unwinged, the base excavated and forming a pit in the adaxial portion of the junction between the petiole and the stem; lamina drying yellowish-orange adaxially and greyish-brown abaxially, 9.2 – 15.4 × 0.9 – 2.5 cm, narrowly lanceolate or elliptic, sometimes falcate, base attenuate, apex acute to attenuate, margin slightly revolute; primary vein complete along entire length of lamina, the intramarginal vein 0.5 – 1 mm from the margin, secondary veins (8 –) 12 – 15 pairs, 0.3 – 0.8 cm irregularly spaced apart, 30° – 40° angle to primary vein, sometimes not visible, when visible prominent abaxially and flat to slightly prominent adaxially; resin ducts visible when dry in the abaxial surface, somewhat intermittent and reticulating, nigrescent lines. Staminate inflorescences 4 – 6 × 4.5 – 6.2 cm, compound dichasium with 2 ramifications per node and a total of approx. 9 – 20 flowers, peduncle 1 – 2.5 cm, cylindrical; pistillate inflorescences 1.7 – 2.3 cm, uniflorous, bearing 3 internodes, each subtended by a pair of bracts, peduncle 0.5 – 0.7 cm; staminate and pistillate inflorescences with paired bracts subtending the inflorescence branches and bracteoles subtending the flowers, 1 – 2 mm, deltate, apex acute, abaxially keeled; pedicels 4 – 8 mm long. Flower buds 4 – 5 mm in diam., green. Staminate flowers non-resiniferous, the perianth differentiated into sepals and petals; sepals 4, 4 – 5 × 4 – 5 mm, concave, suborbicular; petals 4, 3 – 4 × 3 – 4 mm, pink – dark pink, obovate, imprint of stamens visible on the adaxial surface; androecium quadrangular 3 × 3.5 mm; stamens 30 – 47, arranged forming an X or a square with convex sides when viewed from the top; filaments < 0.5 mm long in mature bud; anthers 0.6 – 1.5 mm, longitudinally dehiscent (Fig. 1). Pistillate flowers non-resiniferous, the perianth as in staminate flowers; gynoecium with 4 pairs of stamen-like staminodia, the filaments of the paired staminodia connate only at the very base; stigmas apical, 4, discoid, sessile (Fig. 2). Fruits with sepals persistent, 3 – 5.8 × 1.5 – 4.2 cm, ovoid or ellipsoid, smooth; seeds c. 5 mm, ellipsoid; aril pale greenish-yellow to yellow.

Fig. 1.
figure 1

Clusia salicifolia. A habit of flowering staminate branch; B inflorescence; C detail of abaxial surface of leaf showing resin canals; D abaxial view of sepal; E adaxial view of petal; F stamens; G lateral view of flower bud; H view of androecium from above; J lateral view of androecium showing anthers in compressed form; K detail of inflorescence. A – C based on G. Herrera, E. Moya & P. Kuss 8812 (♂) (holotype K); D – K based on L. Roselli 22 (♂) (USJ). drawn by juliet beentje.

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Fig. 2.
figure 2

Clusia salicifolia. Mature pistillate flower showing staminodes around mature gynoecium, based on E. Mora & E. Rojas 1613 (♀) (CR!, MO!).

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recognition. Clusia salicifolia is distinctive from the majority of other Clusia species due to its narrowly lanceolate or elliptic, sometimes falcate, leaves, with an acute to attenuate base and apex. The leaves of the closely related but allopatric C. falcata Hammel have a similar shape and size to C. salicifolia, however they display fewer secondary veins (5 – 8 vs 12 – 15 pairs) at a narrower angle to the primary vein (20° – 30° vs 30° – 40°). The layout of the resin canals in the lamina also differs between the two species, in C. falcata the resin canals are more or less continuous, whereas in C. salicifolia they are visible on the abaxial surface as mesh-like, reticulating and somewhat intermittent lines (Fig. 1). Additionally, C. falcata produces greenish-white resin, whereas C. salicifolia has colourless resin, and C. falcata has fewer stamens (22 – 24 vs 30 – 47). The holotype of C. salicifolia had been tentatively included as part of C. dukei Maguire (Hammel 2010) but is here separated from that species by its smaller flower buds (6 – 8 mm in C. dukei vs 4 – 5 mm in C. salicifolia) and mostly narrower leaves (2.5 – 5.5 cm vs 0.9 – 2.5 cm). The fruit morphologies of C. salicifolia and C. torresii Standl. are similar, both having an ellipsoid to ovoid fruit shape with persistent sepals. However, fruits in C. torresii have 6 stigmas while those of C. salicifolia have 4. Furthermore, the two species can be readily distinguished by their leaf morphology, C. torresii exhibiting elliptic to oblanceolate leaves with a broadly acute to obtuse or rounded apex, which are never as long and narrow as those of C. salicifolia.

distribution. Clusia salicifolia is distributed in northeast Costa Rica and west Panama (Map 1).

Map 1.
figure 3

Distribution map of Clusia salicifolia.

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specimens examined. costa rica. Alajuela, San Carlos. Calle Damas, bosques aledaños al Río Aguas Zarcas, 600 – 700 m, 24 Sept. 1998, A. Rodríguez, L. Vargas, P. Hurtado & J. Mendez 3615 (♂) (CR!, MO!); Cartago, Turrialba. P.N. Barbilla Cuenca del Matina, sendero principal hacia Barbilla 300 – 400 m, 18 Sept. 2000, E. Mora & E. Rojas 1613 (♀) (CR!, MO!); Heredia, Canton of Sarapiqui, c. 8 km SW of Horquetas, from Finca El Plástico to c. 1.5 km NE thereof, 450 – 550 m, 14 Feb. 1986, M. Grayum & P. Sleeper 6520 (♀) (CR!, MO!); c. 600 m, 21 April 1988, B. Hammel & R. Robles 16711 (♀) (CR!, MO!); B. Hammel & R. Robles 16712 (♂) (CR!, MO!); Finca el Plástico, 12 km SW of Horquetas de Sarapiqui, mature rainforest, 570 m, 21 Sept. 1987, L. Roselli 22 (♂) (USJ!); Rara Avis, c. 15 km SW of Horquetas, Cañon Road, near Atelopus River, 400 – 600 m, 11 Jan. 1989, O. Vargas 262 (♂) (CR CR1559892!, CR156924!, MO!); Limón, Pococí. P.N. Braulio Carillo, Quebrada González, por senderos Ceiba y de la estación, 400 – 500 m, 22 Aug. 2009, B. Hammel & I. Pérez 25289 (st — fruits observed but not collected) (CR!); Talamanca. Camino entre Amubri y Soki; cabeceras del Río Ñabri, 280 m, 4 July 1989, G. Herrera 3133 (♀) (CR!, MO!). panama. Bocas Del Toro, La Fortuna area; 6 miles N of continental divide; in forest along W side of highway, 600 m, 4 March 1986, B. Hammel, G. McPherson & L. Sanders 14574 (♀) (MO!).

habitat. Clusia salicifolia grows on trees, often along rivers or streams, in tropical rainforests at 280 – 700 m.

conservation status. We estimate the EOO for Clusia salicifolia to be 4,943 km2 and the AOO to be 28 km2. Most of the collections from Costa Rica were made in Barbilla and Braulio Carrillo National Park or private reserves close-by, therefore, the stability and conservation of plant populations of C. salicifolia in these areas should be ensured. The specimen from Panama was collected near a main highway in an area subject to recent clearing and forest loss (Potapov et al. 2017). Given the small AOO, small number of locations, and continued estimated decline in quality of habitat of some populations, here we provisionally assess (IUCN 2022) C. salicifolia to be Endangered [EN B2ab(iii)].

phenology. Clusia salicifolia was collected with flowers and flower buds in January to April and September, and collected or observed (B. Hammel & I. Pérez 25289) with fruits in February to April and July.

etymology. The specific epithet salicifolia refers to the leaf shape, which is similar to those of the genus Salix (willow trees) and unusual for the genus Clusia.

notes. The presence of non-resiniferous flowers with a quadrangular perianth, androecium bearing free stamens, gynoecium with staminodia that resemble anthers as well as the elongated pendant fruits, suggest that Clusia salicifolia is part of the Flava group, an informal infrageneric grouping of closely related species mostly distributed in Central America, with a few representatives in the Antilles (Hammel 1986). Preliminary phylogenetic reconstructions based on molecular data suggest that the Flava group is monophyletic, although species evolutionary relationships within the group remain unclear, mainly due to limited taxon sampling and low phylogenetic resolution (Gustafsson & Bittrich 2002; Herbert-Doctor et al. 2021; Luján 2019).

The earliest specimen of Clusia salicifolia was collected 37 years ago, and the most recent is 14 years old. These plant materials have been stored in herbaria for decades and they now provide the fundamental resource to recognise a new species that can, therefore, be properly managed and conserved. The description of this new species from herbarium specimens demonstrates the critical importance of natural history collections as unmatched repositories of biodiversity data, which are fundamental to influence and inform conservation efforts. Furthermore, C. salicifolia is here assessed as an endangered species, which highlights how species could go extinct even before being scientifically described. The extinction of undescribed species, also known as dark extinctions (Boehm & Cronk 2021), reveals that we are inadvertently losing potential key pieces of nature-based solutions to addressing ongoing and future challenges to human livelihoods. We argue that supporting field campaigns aiming to collect biological specimens and their associated data is urgent, as these collections may provide the only pieces of evidence of the existence of many organisms that likely will go extinct in the near future, given the current pace of global biodiversity loss.

Key to Clusia salicifolia and related narrowed leaf species in Central America

  • 1a.Leaves with resin canals more or less continuous and parallel to secondary veins, endemic to Chiapas, Mexico ..... C. falcata

  • 1b.Leaves with resin canals intermittent, branching to mesh-like, distributed in Southern Central America ........ 2

  • 2a.Leaf apex broadly acute to obtuse or rounded ..... C. torresii

  • 2b.Leaf apex acute to acuminate .... 3

  • 3a.Distributed at elevations 1300 – 2000 m in Costa Rica and Panama, leaves elliptic to narrowly lanceolate and (sometimes) falcate .... C. dukei

  • 3b.Distributed mostly at elevations 250 – 600 (– 1800 m) in Costa Rica and Panama, leaves narrowly lanceolate .. C. salicifolia