The Caribbean archipelago is a biodiversity hotspot with high levels of endemism and threatened taxa (Myers et al. 2000). The British Virgin Islands (BVI) and the neighbouring US Virgin Islands (USVI) are a group of Caribbean islands which share many botanical similarities, including several endemic plant species (Acevedo-Rodriguez 1996, Heller 2019).

Solanum conocarpum Dunal was previously thought to be endemic to the island of St. John in the USVI (Acevedo-Rodriguez 1996). The species was described by Dunal in 1813, based on material collected by French botanist, Louis M. Richard at Coral Bay, St. John in 1787. The species was believed to be extinct as it remained uncollected for over a century until it was rediscovered by Pedro Acevedo-Rodríguez as part of his work on the Flora of St. John (Acevedo-Rodriguez 1996, U.S. Fish and Wildlife Service 2019). In 2002, a new subpopulation was discovered at Nanny Point on St. John, revealing many more individuals than initially thought (U.S. Fish and Wildlife Service 2019). In June 2018, a juvenile plant with vegetative characters matching the species was collected (M.A. Hamilton, #1758, DNA Silica Bank S3977, K!) during a botanical survey at Sabbath Hill on the island of Tortola (BVI). Later that year, a targeted survey to the same location was unable to locate the original plant; however, further exploration in the surrounding forest revealed several plants of S. conocarpum, including flowering (Fig. 1) and fruiting (Fig. 2) individuals. Vouchers collected (N. Harrigan, #155, K000817185, K!; #156, K000817186, K!) confirmed the range expansion of this species to the island of Tortola (Heller et al. 2018). Despite belonging to different jurisdictions, the islands of Tortola (British Virgin Islands) and St. John (US Virgin Islands) are separated by less than 2 km of water at their nearest points.

Figure 1.  

Flower of Solanum conocarpum on recently discovered plants on the island of Tortola, BVI. Image by Thomas Heller.

Figure 2.  

Developing fruit on a recently discovered plant of Solanum conocarpum on the island of Tortola, BVI. Image by Thomas Heller.

Solanum conocarpum is a small shrub which can grow up to 3 metres tall in the wild. The leaves are oblong-elliptic or oblanceolate, ranging in size from 3.5 to 7.0 cm long and 1.6 to 3.0 cm wide, coriaceous, glabrous, except for new growth and with a conspicuous orange to yellow midvein. The flowers are heterostylous (Fig. 3), growing in nearly sessile lateral or terminal cymes. The corolla is about 2 cm wide with five violet coloured petals. The fruit is a berry, ovoid conical in shape, green when immature and turning yellow when ripe (Fig. 4) (Acevedo-Rodriguez 1996, U.S. Fish and Wildlife Service 2019, PBI Solanum Project 2020). Solanum conocarpum occurs in dry deciduous and coastal forests with a varied range of associated woody species that lack a characteristic species composition. The species usually grows as an understorey plant responding favourably to disturbance (Stanford et al. 2013, Lindsay et al. 2015, Heller et al. 2018). A habitat suitability model for this species, for the island of St. John, identified 695 hectares of high-quality habitat, 1,275 hectares of moderate-quality habitat, 2,912 hectares of low-quality and poor-quality habitat and 187 hectares of unsuitable habitat (Palumbo et al. 2016). Some of these areas have already been surveyed but a full validation of this model is needed (Monsegur, pers. obs. 2021).

Figure 3.  

Long-styled (left) and short-styled flowers (right) of Solanum conocarpum. Images by Omar Monsegur.

Figure 4.  

Ripe yellow fruit of Solanum conocarpum. Image by Omar Monsegur.

Previous studies by Stanford et al. (2013) suggested that individuals of this species are self-incompatible, possiby due to stigmatic differences between flowers, rather than genetic-based self-incompatibility. However, recent observations of isolated, cultivated material have shown certain individuals to be self-compatible, producing copious fruits, bearing viable seeds and producing abundant seedlings below the mother plant (U.S. Fish and Wildlife Service 2019). The lack of evidence of natural recruitment cannot be attributed to low seed viability as germination under greenhouse conditions has been recorded at almost 100% (Stanford et al. 2013). Under greenhouse conditions, the species can reach a reproductive size between 7 to 16 months from germination (Anderson et al. 2015; Gibney, pers. obs. 2021); however, this period is expected to be greater in the wild due to environmental stochasticity. In addition, exotic mammals are probably limiting seedling establishment by directly grazing on young plants and modifying the structure of the vegetation, which may also result in changes in microhabitat conditions that may affect seed germination and seedling recruitment of this species (Island Conservation 2018, U.S. Fish and Wildlife Service 2019).

Regarding possible pollinators for this species, there are reports of Xylocopa mordax Smith, 1874 and Apis mellifera Linnaeus, 1758 actively visiting the flowers. These observations were followed by a massive fruit production event, suggesting these insects may be effective pollinators for S. conocarpum. Seed disperser vectors for this species remain unknown (U.S. Fish and Wildlife Service 2017, U.S. Fish and Wildlife Service 2019). Recently, Exomalopsis bahamica Timberlake, 1980, a native Caribbean bee, has been observed visiting cultivated material on Puerto Rico (Fig. 5) (Monsegur, pers. obs. 2021). Further research is needed to determine the reproductive biology and confirm the field observations.

Figure 5.  

Solanum conocarpum flower being visited by Exomalopsis bahamica, a bee native to the Caribbean. Image by Omar Monsegur.

There are regional ex-situ collections established on the island of St. John and at St. Georges Village Botanical Garden on the island of St. Croix, both in the USVI and at the J.R. O’Neal Botanic Gardens on the island of Tortola in the BVI (Hamilton et al. 2018, Heller et al. 2018, Island Conservation 2018). Additionally, the species is under cultivation at the Fairchild Tropical Botanical Garden in Miami, USA. The majority of these collections are of material collected and propagated from the island of St. John (Gibney, pers. obs. 2021). The material at the J.R. O’Neal Botanic Gardens was propagated by cuttings and seed germination. Cuttings were taken from plants originally from St. John (Gibney, pers. obs. 2021) and from wild plants from the recently discovered site at Sabbath Hill on Tortola. These cuttings were propagated in perlite with a powder rooting hormone treatment. Once rooted, the cuttings were transferred to a commercial potting media. Seeds were also collected from the population located in Sabbath Hill on Tortola and sown in sterilised commercial potting media without any seed threatment and good germination success was recorded (Fig. 6). Flowers from cultivated plants seem to display a wider variation in size and colour than plants found in the wild. Plants cultivated in a private collection on St. John displayed flowers ranging from white (Fig. 7) to purple (Gibney, pers. obs. 2021). However, white-flowered plants have never been observed in wild populations.

Figure 6.  

Recently propagated sapling of Solanum conocarpum grown from the seeds wild-collected at the J.R. O'Neal Botanic Gardens on Tortola, BVI. Image by Michele Dani Sanchez.

Figure 7.  

Ex situ collection of Solanum conocarpum displaying a white flower. Image by Omar Monsegur.

In the USVI, the US Fish and Wildlife Service is working with the National Park Service (NPS) and local partners, including Friends of the Virgin Islands National Park, on the propagation, population enhancement and species reintroduction on St. John. Additionally, the US Fish and Wildlife Service is also collaborating with Island Conservation (IC) on research to address the role of feral ungulates and invasive plant species on the lack of natural S. conocarpum recruitment (Island Conservation 2018).

The common name of S. conocarpum is "Marron Bacora" (Acevedo-Rodriguez 1996). "Marron" from the French language means “wild”, a term originally used to describe escaped enslaved people who were living in the wild. In the Taíno language, an Arawakan language spoken by the Taíno people who lived in the Caribbean, there is a similar word “Simaran” and, in Spanish, an equivalent term "Cimarron", both with a similar meaning. During the 18^th and 19^th centuries, the common name for sweet bananas used in the Virgin Islands was "Bacova". Many people detect a strong banana-like fragrance to the ripe fruit of S. conocarpum, which was presumably consumed by humans, like the other woody native Solanum species. It seems possible that the single-letter difference was a transcription error or a slight variation in pronunciation (Gibney, pers. obs. 2021).

To gather information for the following conservation assessment, collections from the K, NY and US herbaria and many literature records have been digitised. Field observations contributed additional information on distribution, preferred habitat, threats and population sizes.

Despite many decades of botanical exploration, knowledge gaps on the native flora of many of the UK Overseas Territories (UKOTS) remain (Clubbe et al. 2020), highlighting the need for frequent and continued botanical surveys. For more than twenty years, Kew’s UKOTs team and the National Parks Trust of the Virgin Islands (NPTVI) have been actively surveying the islands of the BVI Archipelago, consolidating botanical knowledge and assessing conservation needs. Over the past decade, Kew and NPTVI have also been working closely with regional partners, such as US Fish and Wildlife Service (USFWS), the Puerto Rico Department of Natural and Environmental Resources and the University of Puerto Rico to survey, study and conserve threatened and endemic plant species. Our collaborative and intensive survey efforts are now resulting in many new discoveries: new species records, range extensions and new plant records for the region. The discovery of S. conocarpum on Sabbath Hill on the island of Tortola is an example of the benefit of continued regional surveying efforts.

Strong regional collaboration is needed to conserve species such as S. conocarpum that cross international borders and prevent their extinction. Future conservation efforts should prioritise the exclusion or population control of feral animals within the species' habitat as this is the main threat to the viability of S. conocarpum populations. In addition, research on population genetics across the species range is needed to provide information for future propagation and reintroduction efforts. For the time being, this species is assessed as Endangered (EN), based on Criteria B1b(iii,v)+2b(iii,v)+C2a(i), according to the IUCN Red List Categories and Criteria (version 3.1) and guidelines (IUCN Standards and Petitions Committee 2019).

We are grateful to the National Parks Trust of the Virgin Islands in the BVI, especially Dr Cassander Titley-O'Neal and Ms Nancy Woodfield-Pascoe for their continued support and assistance. Thank you to Ms Nancy Woodfield-Pascoe for comments on an early version of this manuscript. Thanks to Dr Sandy Knapp and Dr Pedro Acevedo-Rodriguez for their invaluable knowledge and specimen identifications. We would also like to thank James Yrigoyen of USFWS, Cielo Figuerola and José Luis Herrera of IC and Shane McKinley of US Department of Agriculture (USDA). The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the US Fish and Wildlife Service. Use of trade names in this article does not imply endorsement by the United States government.

Fieldwork: all authors; data anlaysis and writing the article: SB, OM, TMH, NH, EG and MAH; finalising the text: all authors.

There are no conflict of interest.