Citizen science records are fuelling exciting discoveries of new plant species

Abstract

Each year, approximately 2000 to 2500 plant species are described as new to science (Cheek et al., 2020). However, there are still, at a minimum, tens of thousands of undescribed plant species (Heywood, 2017). Many of these have already been collected, with numerous recently named species described from specimens collected and deposited in herbaria decades—or even centuries—ago. Many more undescribed species still reside as vouchers in herbaria, waiting to be examined and recognized as novel, highlighting the immense importance of these institutions for understanding plant diversity globally.

There are also many undescribed species remaining to be discovered in the field. Traditionally, an important “discovery pathway” for these taxa has been formal collecting expeditions conducted by professional botanists. In some cases, the discovery and description of taxonomic novelties is a primary expedition goal (e.g., Bush Blitz in Australia; Preece et al., 2015). However, for many expeditions, species discovery is just one goal competing with others, including the collection of tissue samples for genomics, ecological monitoring, and the possible rediscovery of potentially extinct species. Furthermore, resources and funding dedicated to discovering new species are limited; finding new opportunities for species discovery is therefore essential.

One such opportunity for discovery is via the citizen science platform iNaturalist (www.inaturalist.org; see Mesaglio, 2024), one of the largest sources of contemporary plant occurrence data globally. As of March 2025, over 92 million verifiable records of plants have been uploaded to iNaturalist from around the globe, covering approximately 172,000 identified species submitted by 2.4 million observers. In addition to the hundreds of scientific papers that use iNaturalist data for ecological and conservation studies, at least 12 new plant species have been discovered, and subsequently formally described, since 2022 through records uploaded to iNaturalist. In some cases, these species had already been collected decades ago, but the specimens had been overlooked or identified as an already described species, while in other cases, the iNaturalist observations were the first known records of those species. Excitingly, these species cover a variety of growth habits, taxonomic groups, vegetation communities, and regions (Figure 1) ranging from a shrub in Rutaceae from the thorn forest of Mexico (Megastigma acarrilloi; León, 2024), to a geophyte in Iridaceae from the fynbos of South Africa (Moraea anastasia; Manning et al., 2025), to a mycoheterotrophic herb in Thismiaceae from moist riparian forest in Colombia (Thismia paradisiaca; Guzmán-Guzmán and Plata-Torres, 2023). All of these cases, however, are united by a critically important common denominator: each species was only recognized as novel because of expert engagement with iNaturalist.

In all published cases thus far, the significance of each observation was only realized once it was seen by an expert. In the specific context of this paper, we define “expert” as a botanist or taxonomist with the knowledge to recognise potential taxonomic novelties from images (see Mesaglio et al., 2025 for further discussion on defining an expert). Expert encounters with potential novelties on iNaturalist broadly fall into one of three categories: (1) finding the record “incidentally” during regular identification efforts, (2) encountering the record during a more systematic review of all records in a focal taxon as part of a revision or other manuscript, or (3) being directly tagged in or notified about the record by another user soliciting expert feedback. We make two important recommendations for experts based on these different pathways to unearthing taxonomic novelties.

First, there is high value in experts routinely reviewing iNaturalist observations in their area of expertise, regardless of whether they are actively working on a revision or new descriptions (Mesaglio et al., 2025). Tens of thousands of new plant records are uploaded to iNaturalist every day from around the globe, so regularly browsing records, whether daily, weekly, or monthly, maximizes the chances that significant records are found and recognized in a timely manner. The near-constant influx of new records increases the chance of serendipitous discoveries, especially for taxa in regions with many observers, but only if there are experts actively curating these records (e.g., the geophyte Moraea saxatilis was recognized as a taxonomic novelty through review of an observation identified by the observer as “Iridaceae”; Manning and Goldblatt, 2024).

Second, it is important for experts to regularly interact with the iNaturalist community and build awareness of their field of expertise among the broader userbase of amateur naturalists and other experts. One of iNaturalist's great strengths is the facilitation of real-time interactions between users from around the globe, and once an expert has established their area of expertise, other users will notify them of potentially significant records. However, developing these collaboration networks requires time and effort. Regularly identifying records, including described and common species, and actively interacting with other users helps to build awareness and appreciation of expertise among the community, and cultivates a strong culture of sharing records with experts to solicit their input (e.g., the hemiparasitic herb Castilleja salaisolaveae was recognized as a taxonomic novelty after an expert was tagged in an observation by the observer; Egger et al., 2022).

In addition to experts serendipitously encountering records of new plant species, there is also scope for more proactive facilitation of species discovery. We strongly emphasize the importance of meaningful collaborations between experts and observers of putative novelties. For example, experts can offer iNaturalist contributors coauthorship on papers describing new plant species (or even lead authorship for users who may also be scientists with expertise in the field). These collaborations help provide local scientists and naturalists with invaluable opportunities to contribute to and lead research (Adame, 2021). Researchers can identify plant diversity “darkspots” (regions containing many undescribed and unrecorded species, sensu Ondo et al., 2024) and reach out to relevant “superusers” and other motivated citizen scientists from these regions. Experts can provide guidance on when to conduct searches, which habitats should be targeted, and which characters are important to photograph. Ideally, citizen scientists can also collect specimens for deposition at herbaria provided the appropriate permissions and licensing have been obtained. Experts can provide guidance for inexperienced users on how to make collections, including what makes a good herbarium specimen and when to think twice for rare species or populations.

We highlight two key directions towards which experts can direct the efforts of citizen scientists. First, there is high value in promoting exploration for ephemeral species that may only appear for a limited time after specific conditions, or species which only form reproductive parts necessary for identification rarely and for short times. One challenge for professional botanists is limited time and resources, making it difficult to rapidly respond to events like bushfires or unusual rainfall events, especially in remote areas, which may create ideal conditions for ephemeral species or flowering episodes. Collaborating with the widespread network of iNaturalist users offers an effective solution. For example, Ovicula biradiata (Asteraceae), a newly described genus and species discovered via iNaturalist, is an ephemeral and range-restricted species that was found in a remote tract of Big Bend National Park in the United States by a citizen scientist searching for rare plants in remote terrain (Manley et al., 2025). Harnessing this enthusiasm and desire to contribute to the natural sciences will be a key future direction for expert botanists.

Second, a strong emphasis can be placed on taxa where diagnostic characters are better captured by photographs of live plants rather than preserved voucher specimens. In situ photographs of flowering individuals uploaded to iNaturalist facilitated the discovery of Caesia walalbai (Hemerocallidaceae) in eastern Australia, as perianth and staminal filament color are important characters within this genus (Webb et al., 2023). Numerous specimens of this taxon had already been collected dating back to the 1950s, but these had previously been determined as a more widespread species, and their novelty overlooked because of the loss of floral color when dried. Similarly, Stenostephanus purpureus (Acanthaceae) was recently recognized as a distinct species and separated out from S. silvaticus thanks to photographs uploaded to iNaturalist. A comparison of images of S. silvaticus sensu latu from Mexico and Costa Rica revealed important differences in corolla limb shape and inflorescence axis and corolla color that are often lost or not apparent on many herbarium specimens. Reexamination of herbarium specimens revealed more differences further supporting the description of S. purpureus as a new species restricted to Costa Rica and Panama. There have also been cases where undescribed species were already known from collections, but the discovery of high-quality images of reproductive material on iNaturalist facilitated further specimen collection and subsequent description (e.g., Alvarado-Cardenas et al., 2020).

Given the almost 600 known plant extinctions since 1753, and that undescribed and recently described plant species are more likely to be threatened with extinction (Humphreys et al., 2019), there is a strong imperative to accelerate plant species discovery to avoid the extinction of taxa before they are known to Western science. The emergence of iNaturalist as one of the largest sources of plant occurrence records globally has provided a valuable new opportunity for discovering new plant species. By tapping into this resource, expert botanists have the opportunity to build meaningful collaborations with other researchers, naturalists, and citizen scientists from around the world, and help to build our understanding of Earth's flora.

T.M.: Concepualization, Data curation, Investigation, Visualization, Writing – original draft; H.S.: Conceptualization, Writing – review and editing; W.K.C.: Conceptualization, Writing – review and editing.