Systematics, natural history, and conservation of Erica (Ericaceae)

Abstract

Worldwide, many tens of thousands of plant species are threatened with extinction in the wild. Those that are naturally rare or have narrow distributions are particularly vulnerable. The flowering plant genus Erica is a prime example, its numerous species presenting additional challenges associated with conserving large, complex, plant groups. This topical collection of papers represents a substantial body of research on inter-dependent themes in nomenclature, taxonomy, phylogeny, ecology, and conservation of Erica species. It will serve as a lasting resource and reference, helping us to better understand, describe, and name species diversity and improving our knowledge of the complexity of ecological interactions in the wild. These advances will aid and champion conservation of natural habitats and support targeted efforts to secure the most critically endangered species in seed banks and botanic gardens.



In this topical collection, we present 12 interlinked papers on the nomenclature, taxonomy, phylogeny, ecology, and conservation of species of the large flowering plant genus Erica (Ericaceae). The numerous species of Erica are concentrated in South Africa’s spectacular Cape Floristic Region (Oliver et al. 1983), but with diversity extending through Africa (Beentje 2006), Madagascar (Perrier de la Bathie 1927), and into Europe (Nelson 2011). Many are naturally rare or have narrow distributions, placing them amongst the sobering proportion of plant species worldwide that are threatened with extinction in the wild (Lughadha et al. 2020). Despite its relatively young age, the genus harbours a tremendous morphological diversity, most notably in floral traits (Rebelo et al. 1985). Apart from pollinator-driven differentiation (e.g. Johnson 1996; Musker et al. 2024), its enormous species richness is associated with the seeder post-fire response in areas with high winter rainfall reliability (e.g. Ojeda 1998; Cowling et al. 2018). The collection includes reviews and syntheses consolidating existing knowledge and making it findable and accessible, as well as original research and novel data. Their collective aims are to better understand, describe, and name Erica species diversity, to enable accurate identification, to understand their ecological interactions in the wild, and to support their conservation.

Progress in understanding the evolution of any lineage depends on sound taxonomy, especially for a large genus such as Erica that includes groups of species characterised by relatively minor morphological differences, and which has a long history of horticultural innovation with numerous cultivars. The work of Elliott et al. (2024) is fundamental, providing an authoritative reference for Erica names through the World Flora Online (WFO), which is regularly updated and maintained by the Taxonomic Expert Network for Ericaceae. During the process of integrating data from the International Register of Heather Names (Nelson and Small 2000, 2004) into WFO, Nelson et al. (2023) clarified longstanding issues in Erica nomenclature, replacing 13 illegitimate names for Cape species. In June 2024, WFO listed 851 accepted Erica species. Of those, 65% were represented in a phylogenetic analysis by Pirie et al. (2024) used to identify Evolutionarily Distinct and Globally Endangered (EDGE) species (Isaac et al. 2007). The WFO data now forms the taxonomic backbone for a revitalised version 4 of the Erica ID aid (Oliver et al. 2024). This, in turn, has been updated to incorporate data on the poorly understood Malagasy Erica diversity (Hackel et al. 2025). It has also been used as a morphological comparative tool, in combination with the phylogenetic information provided by Pirie et al. (2024), to assess and describe novel taxa in Cape Erica (Hoekstra et al. 2025).

The development of molecular systematics and implementation of novel methods can reveal great insight into species-level systematics. Musker et al. (2025) presented new Ericaceae-specific hybrid sequence capture markers and resources for phylogenomic inference in rapidly diverged lineages and species complexes. Rodríguez-Buján et al. (2024) used a different high-throughput sequencing approach, analysing single nucleotide polymorphisms from shorter RADseq sequences, combined with morphology, to test species boundaries in two European species. They could confirm the status of the narrow endemic Ericaandevalensis. Pasta et al. (2025) provided detailed documentation for a further European species: Ericasicula, which occurs across the Mediterranean basin, but shows a highly fragmented distribution pattern.

The evolution of floral diversity requires thorough understanding of plant-pollinator interactions. Two works, by McCarren et al. (2024) and by Van der Niet and Cozien (2024), improved our understanding of the complex interactions of Erica species with their pollinators. Beyond the field of pollination ecology, this work serves to illustrate the importance of species conservation to preserve ecological interactions in native habitats.

Improving the existing tools for species identification aids in research and public engagement in biodiversity conservation. The Erica ID aid will continue to be an essential resource for both amateurs and professionals attempting to identify Erica species, and there is a clear route to further improvement. For example, more of the subspecific taxa can be coded, and better distribution and phenology data, as well as documentation of other diagnostic traits, would further enhance its performance (Oliver et al. 2024; Hoekstra et al. 2025). There remains undescribed diversity, even in the already recognised enormous richness of Cape Erica, and a substantial shortfall in phylogenetic data for African and Madagascan diversity (both representation of taxa and resolving power of the most widely used markers), without which it is more difficult to identify EDGE species with confidence. Direct evidence for pollinators of Erica species is limited. For threat status, we still rely on the foundational work of Raimondo et al. (2009). This now needs updating and expanding, particularly for endangered and data-deficient taxa. The situation described by Hackel et al. (2025) for Malagasy Erica represents the starkest knowledge gap: we must resolve uncertainty in species limits and specimen identifications as an urgent prerequisite to formal threat assessments.

Together, this set of papers presents both individual advances and a clearer view of knowledge gaps. We are now in a stronger position to translate existing knowledge and resources into priorities for action, to more effectively obtain and target funding for conservation efforts in natural habitats, and to secure the most critically endangered species in seed banks and botanic gardens (Pirie et al. 2022). We believe that the synergy created through taxon-specific topical collections such as this is hugely beneficial for advancing both systematics and its dependent disciplines and endeavours.

Expanding knowledge of large genera requires dedicated scientists who push the existing boundaries during lifelong carriers. In working towards this collection, our aim was to provide lasting resources and reference for future work, but also to honour the enormous contribution to Erica taxonomy of our longstanding collaborator E.G.H. (Ted) Oliver and his late wife Inge M. Oliver. This is described in a dedicated review article by Nelson et al. (2024). Ted sadly passed away in January 2025. He was recently honoured with another species (Eulophiaedwardii Bytebier; Bytebier and Grieve 2025) described in Orchidaceae, his other group of special interest. We could also not have anticipated the loss of E. Charles Nelson, both author and editor on this collection, in May 2024. His documentation and clarification of Erica nomenclature over many years, as well as his authoritative monograph of the northern species (Nelson 2011), was just part of a remarkable body of work (Shaughnessy 2024) and his productivity showed no signs of slowing. This collection is therefore dedicated with immense gratitude to Ted, Inge, and Charles.

Citation

Pirie MD, Coetzee A, Fagúndez J, Forest F, Musker S, Nelson EC, van der Niet T, Ojeda F (2025) Systematics, natural history, and conservation of Erica (Ericaceae). PhytoKeys 257: 119–124. https://doi.org/10.3897/phytokeys.257.159429

Additional information

Conflict of interest

The authors have declared that no competing interests exist.

Ethical statement

No ethical statement was reported.

Funding

No funding was reported.

Author contributions

Edited the topical collection: all authors; drafted the text: MDP; commented and approved text: all authors except ECN.

Author ORCIDs

Michael D. Pirie https://orcid.org/0000-0003-0403-4470

Anina Coetzee https://orcid.org/0000-0002-1646-557X

Jaime Fagúndez https://orcid.org/0000-0001-6605-7278

Félix Forest https://orcid.org/0000-0002-2004-433X

Seth Musker https://orcid.org/0000-0002-1456-1373

E. Charles Nelson https://orcid.org/0000-0002-3909-4388

Timotheüs van der Niet https://orcid.org/0000-0002-5250-8995

Fernando Ojeda https://orcid.org/0000-0001-5480-0925

Data availability

All of the data that support the findings of this study are available in the main text.