by Jinlong Zhang

When you come across a plant and want to know its name, is there a quick and accurate way to achieve this?

If you're a plant lover, you may have joined a social media group where you can post a photo and group members who know the plant can tell you its name. Of course, as we cannot be sure the names given by others are accurate or not, we still must check the information for verification. But what if you've never belonged to such a group?

As the saying goes “there’s an app for that”! Almost everything you want to do can be achieved with a mobile app, it seems. And plant identification is no different. As long as you can take a photo with your mobile phone, you can take a picture of the plant and scan it into a plant recognition app, which will most times tell you the name of the plant.

Numerous apps are designed to recognise plants, among them PlantNet (https://identify.plantnet.org/zh-hant), iNaturalist (https://www.inaturalist.org/), Xingse (https://www.xingse.net/), Aiplant (https://www.plantplus.cn/cn/tools/1), and even WeChat has such a function.

So, are the results given by mobile apps accurate?

A few years ago, Professor Ma Keping, a researcher at the Institute of Botany, Chinese Academy of Sciences, instructed students to explore the accuracy of eight mobile phone apps that claimed the ability to identify plants, and found that the power of plant identification varied greatly from one to another. In addition to the app itself, the accuracy of the identification depended on the species, and when and where the user encountered it, and whether the plant was blooming and fruiting during identification. Behind the mobile apps are machine learning models trained with photos of plants already identified. Different models, of course, vary in their mechanisms and parameters, which inevitably leads to differences in identification accuracy. For example, most of the photos used in model training mainly cover plants growing on the roadside or in parks, with a limited number of photos of wild plants in their library. It is not surprising that these apps are generally good at identifying cultivated plants, but for wild species the results may not be that accurate, or could even be completely wrong.

In addition to the difficulty of identifying wild plants, mobile apps are obviously not enough for the intellectually curious: even if they can tell you what the plant species is, it will never be able to tell you how and on what basis the plant was identified, as a botanist would.

It seems that ultimately one needs to consult a botanist to accurately identify a certain type of plant, especially wild plants. But how do botanists identify plants? What information do ordinary people need to look up to get the most accurate plant names? To answer these questions, we need to understand how plant names come about.

1. Naming, Describing and Publishing

To find the right name for a plant, you first need it to have a name. If a plant doesn't already have a name, give it a name first. Since each place has its own language or dialect, if you name a plant in a local language or dialect, the name must be easily accepted by the local people, but if you want the name to be accepted by people all over the world, you must follow the latest version of the International Code of Nomenclature for algae, fungi, and plants. This means the plant will have a scientific name, which includes two parts, the genus name, and the species epithetic, both of which are in Latin. This nomenclature is called binomial, and was established by Carl Linnaeus, the father of plant taxonomy, and has a history of nearly 300 years.

At the same time, taxonomists also describe the morphological characteristics of the species, as well as its habitat, flowering and fruiting period, geographical distribution, and conservation status. Moreover, when describing a new species, it is important to point out the significant differences between the new species and similar species, to make it clearer that the species is indeed a new one. All this information must be written in Latin or English, and published in an academic journal so that anyone who studies plants can read it. Only after the species is validly published, can this scientific name be regarded as the ‘admission ticket’ of science.

Figure 1. International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code) Chinese Edition

2. Plant Taxonomists are Experts of Certain Groups of Plants

Currently, more than 350,000 species of vascular plants have been recorded and described worldwide, and the number keeps on increasing at a rate of 1,000-2,000 per year. It is obviously impossible for one person to thoroughly study the names of all plants. Therefore, most botanists focus on a particularly specific group of plants. For example, Dr Stephan Gale of KFBG specialises in Orchidaceae, particularly for species occurring in East and Southeast Asia. Professor Richard Saunders from the University of Hong Kong specialises in the classification and evolution of Annonaceae.

Botanists are so specialised nowadays that it is not surprising that if you pick a plant sample randomly from the wild, even it is a common species, the taxonomist may still have no idea about the plant, and this does not mean that the botanist is ‘not a real expert’.

3. Classification of Species

The complexity of botanical research is also manifested in the fact that different people may have different understandings of species. Usually, there are morphological variations within a species’ natural range, and this leads to disagreement on the classification of species: some botanists believe that it should be one species, while others may think they are different species and all of them should be described. In this case, in addition to carefully studying the morphological differences, it is often necessary to collect more samples to study whether there are morphological transitions between species, whether there is an overlap in the geographical distribution or habitat, or whether there is hybridisation between species, and whether hybrids can produce fertile offspring, and so on. In recent years, techniques such as transcriptome, population genetics and genomics have been more widely used to clarify the relationship between species and explore speciation issues.

4. New Classification Systems

In the past decade, new classification systems based on molecular phylogeny have superseded the old classification systems for all vascular plant groups, including: the APG IV system has superseded the widely used Engler’s system, Hutchinson’s system and Cronquist’s system for angiosperms; the Christenhusz’s system and Y. Yang’s system of gymnosperms have superseded W.C. Cheng’s system; and the PPG I system of ferns and lycophytes has superseded Ching’s system. Compared with the old system, these new classification systems incorporate significant changes. Taking angiosperms as an example, there are Myrsinaceae and Aceraceae both in the Engler’s system and the Cronquist’s system, and some species of these two families are also very common in Hong Kong, while in the APG IV system, all species of Myrsinaceae have been moved into Primulaceae, and all the species of Aceraceae have been placed in Sapindaceae. In other words, Myrsinaceae and Aceraceae do not exist in the APG IV system.

Fig.2, South China Maple, Acer sino-oblongum. In Flora of Hong Kong, it is in Aceraceae, while in the APG IV system, it is in Sapindaceae

Figure 3. Ardisia mamillata Hance, in Flora of Hong Kong, is in Myrsinaceae, but in the APG IV system, it is in Primulaceae

Most of these new systems have been adopted by the world's latest and most authoritative plant databases, such as Plants of the World Online (POWO) and World Flora Online (WFO). The latest publications have also adopted these new classification systems. Due to changes in taxonomic systems, for example, the same species sometimes appears in different families in new systems and in flora that are still widely used -- Flora of Hong Kong, for example, uses Cronquist’s system. In this case, to find out the family for a taxa in the most up-to-date classification systems, in addition to querying the large databases such as POWO and WFO, one can also search the Catalogue of Life China Annual Checklist (http://www.sp2000.org.cn/), Duocet Plant Wiki* (https://duocet.ibiodiversity.net/) and Plant Science Data Centre (https://www.plantplus.cn/cn) maintained by the Institute of Botany, Chinese Academy of Sciences.

The good news is that although the new classification system is significantly different compared to the old system, the basic framework of these new systems is likely to remain relatively stable for a long time to come.

5. Accept Names and Synonyms

In addition to changes in the definition and position of families in classification systems, the changes in scientific names may be more common, and it is not unusual for a plant to have several or even dozens of names. Some of the names widely used in Hong Kong may be subject to change later.

In 1981, André Kostermans, a botanist at the Bogor Botanical Garden in Indonesia, described a new species of Lauraceae in Hong Kong, the voucher specimen of which was collected at Kadoorie Farm by Gloria Barretto in 1977. He named it Persea kadooriei Kostermans, which means “Kadoorie’s Persea” and in Chinese “嘉道理楠”. This Chinese name is still widely used in Hong Kong today. But later, other botanists discovered that as early as 1931-1932, this species was collected by S. P. Ko and Chi Wang of the Botanical Institute, College of Agriculture, National Sun Yat-sen University (later known as the South China Botanical Garden) in Dawuling, Xinyi, Guangdong, and in 1953, the famous plant taxonomist Professor Chun Woon Young named it Machilus wangchiana Chun, and the Chinese name ‘Wong Chi’s Machilus’ is proposed, in honour of Chi Wang (later changed to Xinyi Machilus), was published in the journal Acta Phytotaxonomica Sinica.

If there are two scientific names for the same plant, which one should be used? This brings us to the issue of accepted names and synonyms. According to the rules of priority in plant nomenclature, the accepted name is the earliest validly published name of a plant, so the accepted name of this species can only be Machilus wangchiana, while Persea kadooriei should be treated as a synonym. Of course, there are no rules for the Chinese name of the plant, for example, although the Chinese name of this species is best called Xinyi Machilus (信宜潤楠), one can still call it Kadoorie’s Persea (嘉道理楠), and or even Wang Chi’s Machilus (黃志楠). However, when mentioning this species in science, the accepted name Machilus wangchiana should always be used.

Most flora list a number of synonyms for every species (taxa), and finding out the accepted name of the species and treating other names as synonyms is the plant taxonomists’ job. This is a complicated task, because there are many sources to be consulted, a number of which are 100 to 200 years old, and in addition to English, the documents may also be written in Latin, French, German, Japanese or Chinese, and may be difficult to obtain, hence it usually takes a lot of effort to source them. To a certain extent, plant taxonomy is similar to studying history based on literature, except the latter uses ancient documents to explore the politics, economy, culture and livelihood of the time, while the former mainly explores the changes of a plant’s names. Fortunately, the Biodiversity Heritage Library (BHL) and the Tropicos Online Botanical Database (https://www.tropicos.org/) often provide the full text of historical documents, which provides a lot of convenience for taxonomic research.

Figure 4.  Xinyi Machilus (Machilus wangchiana Chun) is found in Tai Mo Shan, Mount Parker and a few other locations in Hong Kong

Figure 5 One of the type specimens of Machilus wangchiana (according to the China Virtual Herbarium https://www.cvh.ac.cn/)

Figure 6. The original description (protologue) of Machilus wangchiana by Professor Chun Woon Young in 1953

Figure 7. Persea kadooriei is listed as a synonym for Machilus wangchiana in Flora of Hong Kong

6. Herbarium and Herbarium Specimens

In order to study the change of plant names, in addition to being familiar with the taxonomic literature, the most basic materials are the herbarium specimens.

When botanists describe a new species, in addition to giving a new name, they also use at least one specimen as the basis for description, and in the article he or she will indicate the collector and collector’s number of the voucher specimen. This is how the linkage is created and this specimen then becomes the type specimen for this name. The information on the type specimen itself, as well as in the label, is the very first information for a species. Following this practice, every published scientific name of a plant species should link to at least one type specimen. Being the voucher of plant names, type specimens are of great scientific value and are the basis of taxonomy. If there is an unknown plant, and if no significant difference can be observed from the plant in the type specimen, then the two should fall in the same species, and the identity of the ‘unknown’ plant is then ‘clear’.

Type specimens are useful, but there is also a problem: there are more than 3,000 herbaria in the world, and more than 390,000,000 specimens are deposited in these herbaria. Tens of thousands of type specimens are scattered in different herbaria. Also, although some herbaria store the type specimens in the type specimen cabinets, many of the type specimens in other herbaria are still mixed with the ordinary specimens and some effort is needed to find them out. On the other hand, because modern taxonomy originated in Europe, most of the early plant specimens were collected by westerners in the early days, and the specimens were mostly deposited in the herbaria of universities, botanical gardens, or natural museums in Europe, so it is still difficult for botanists to systematically study them. Pre-internet, taxonomists often visited herbaria or borrowed specimens for examination, which was very inconvenient. Fortunately, in the 21st century, many herbaria have their specimens digitised; for example, the Natural History Museum (P) in Paris has digitised most of its plant specimens, and the digitisation of herbarium specimens at Kew Gardens is ongoing. Jstor has also gathered large numbers of photos of type specimens that registered users can access. A considerable number of Chinese herbaria have digitised their herbarium specimens, and most of the photos can be viewed at the Chinese Virtual Herbarium (https://www.cvh.ac.cn/) and the NSII-China National Specimen Information Infrastructure (http://www.nsii.org.cn/2017/home.phpAccess).

Figure 8. Distribution of nearly 4,000 herbaria in the world (according to https://sweetgum.nybg.org/science/ih/map/)

7. Flora and Literature Commonly Used in Hong Kong

The flora in South China has been explored for a long time, and taxa new to science is becoming more and more scarce, although there are still some remaining. In 2021, taxonomists from South China Botanical Garden, Chinese Academy of Sciences discovered the genus Fenghwaia G.T. Wang & R.J. Wang in Nanfeng Mountain, Jiangmen, Guangdong, which is a new genus of Rhamnaceae. In recent years, some new species have also been discovered in Guangdong, and the relevant information is recorded in a dataset on inventory and geographical distributions of higher plants in Guangdong, China, published recently.

Hong Kong has a history of almost continuous plant collection, surveys and research going back to nearly 200 years, thus starting earlier than other parts of China. Initially, it was mainly western missionaries and naturalists who collected in southern China, and, of course, they could set foot in Hong Kong. Between 1852 and 1857, Berthold Seemann compiled a checklist of plants of Hong Kong Island. In 1861, Flora of Hong Kong by the British botanist George Bentham was published in London and was the first modern flora in Asia. In 1912, Stephen Dunn and William Tutcher compiled Flora of Kwangtung and Hongkong (China) based on the results of their in-depth expeditions to Guangdong. From 1962 onwards, the Agriculture, Fisheries Department of the Hong Kong Government (later known as the Agriculture, Fisheries and Conservation Department) published the Check List of Hong Kong Plants, and the revised versions were later published in 1965, 1966, 1974, 1978, 1993, 2004 and 2012. In 2003, Flora of Hong Kong: Pteridophyta was published by KFBG. In 2011, all four volumes of Flora of Hong Kong, edited by Hu Qi-ming and Wu De-lin, were published. In addition, Xing Fu-wu, a researcher at the South China Botanical Garden, collected thousands of herbarium specimens in Hong Kong from 1996 to 1998, and published a list of vascular plants in 2000, which is still an important reference for the conservation status of plant species today. Since the flora and the checklists are compiled based on herbarium specimens, even the old texts are still of great importance in botanical research.

Even though Hong Kong is probably the place with the longest history of botanical surveys in South China, the number of newly recorded plants is still increasing at a rate of several per year, some of which are even species new to science. These discoveries have been published in various publications, and include those reported by Hui-ling Zhu, Jin-gang Liu, Stephan W. Gale and Pankaj Kumar.

Fig. 9 Title page of Flora of Hong Kong, by George Bentham, published in London in 1861 (according to BHL)

In summary, the main work of plant taxonomists is to give names to new taxa, clear up old names, clarify the relationships between various taxa (such as families, genera and species), and report new species in a region, only by doing this can new suggestions for the biodiversity conservation to be made.

8. The General Process of Plant Identification

Returning to the original question, if you encounter an unknown plant, how do you get the most accurate plant name for it? Following are the most common practices.

8.1 Determine the family and genus
If you are familiar with the flora of a certain area, you should directly recognise the plant to the family and genus, which is a common effort and requires at least several years of training and practice. If you can't recognise the family, you can ask an expert to help you identify it. If you can't find an expert, it is probably better to refer to professional websites or mobile apps that use AI for identification, including: PlantNet, CUBG Plant Search Engine (https://image.cubg.cn/), AiPlant and Xingse.

8.2 Check the regional flora or plant checklist to narrow down the search
It is easier to identify plants of a region based on the regional flora because the botanists who wrote the flora have narrowed down the list of species. For Hong Kong, one can refer to Flora of Hong Kong (with colour photos for most of the species), Flora of Shenzhen (each species has a line art, with colour photos for most of the species), Flora of Guangdong, A dataset on inventory and geographical distributions of higher plants in Guangdong, China, Flora Reipublicae Popularis Sinicae and Flora of China.

After getting the flora, the main step is to use the keys to see what species can be retrieved. However, many keys require some of the characters of flowers or fruits, and the requirement is often difficult to meet, and in such cases, the keys would be of little use.

Thus the only way to do it is to exclude species one by one. The quickest method is, of course, to compare the plant with photos or line drawings. Usually, the species should have been included in the regional flora, especially the naturally occurred ones. Only occasionally, if it is not found, it may be a new distributional record, or it is also possible that the identification in the flora was wrong. In this situation, you may need to consult botanists to make corresponding corrections or additions.

8.3 Search for type specimens or photographs of plants identified by experts
Once you have obtained a name, the next step is to compare it with the type specimens, or plant photos identified by experts.
The useful resources are China Botanical Garden Union Plant Photo Search Engine (https://image.cubg.cn/), China Virtual Herbarium (CVH), Jstor Type Herbarium Photo Library, China Natural Herbarium (CFH), China Plant Science Data Centre, as well as iNaturalist and GBIF (https://www.gbif.org/). For plants native to Hong Kong, one can first browse the Hong Kong Plant Database (https://www.herbarium.gov.hk/tc/hk-plant-database/index.html) and HKCWW Plant Website (http://hkcww.org/hkplant/index.php). When comparing whether the plant is different from the type specimen, it is better to pay attention to the morphological characteristics commonly used in distinguishing species, for example, the shape of the leaves, texture, number of lateral veins and type of hairs and so on. It is also important to note that taxonomists may have different views on species classification, and hence the identification of specimens could also be different. It often requires a deeper understanding of the morphological characteristics and research history of the taxa to judge which name is more appropriate.

If there are no significant differences between the plant and the type specimen, it is likely that they are the same species. Otherwise, further relatives under the same genus should be examined. Of course, it is always helpful to examine the specimens of closely related species and the identification will be more accurate accordingly.

For some plant samples, such as sterile material, only limited morphological characteristics can be observed, and for plants in this situation, the sample may be wrongly identified to another genus or even another family. It is always necessary to compare the sample with well-identified specimens carefully to make a better identification.

If you are not familiar with the botanical terms, it is helpful to refer to books such as Plant Identification Terminology: An Illustrated Glossary or The Kew plant glossary: an illustrated dictionary of plant terms. This is particularly true for Orchidaceae, Apocynaceae, Poaceae, Cyperaceae and ferns, because these families or groups have some special terms that require study to understand.

8.4 Determine the accepted name
If all the characteristics of a plant match a type specimen, they are likely to be the same. Although the type specimen must have been used as the original evidence of a scientific name, the scientific name is not necessarily the current accepted name, so it is important to search the name in World Flora Online, Plants Of the World Online, Catalogue of Life China Annual Checklist or other sources to confirm the current accepted name. Reference can also be made to the latest revisions of taxonomists, which are usually published in botanical journals.

8.5 Giving the final identification
In general, once the plant is confirmed, botanists will provide the following information:
• Name of the collector (or photographer)
• Collector’s number (or the photo number)
• The scientific name with the authority
• Name of the person who made the identification
• Date of identification

As you may have noticed, this is exactly what is on the identification label on herbarium specimens. That's right! As research progresses, taxonomists and herbarium curators keep on adding new labels to herbarium specimens: some to verify previous identifications, others to correct old identifications. Ultimately, the name of the plant on a specimen is generally the name determined in the latest identification.

It is also important to note that the name of the last identification is not set in stone. As science continues to advance, the names accepted at present may be treated as synonyms, some synonyms may be changed to accepted names, species new to science will be described and new distribution records will be reported, and even the families and genera of plants may change due to changes in taxonomic systems. The only correct way to ensure the accuracy of the identified name is to refer to the most up-to-date sources and keep track of the latest research.

Identifying plants is fun, but accurately identifying plants requires considerable expertise, serious study, and hard training before you can find the most accurate name. Are you ready to take on these challenges?

*  The classification system of Docet Wiki is based on several modern classification systems but sometimes with minor modifications, therefore, it is more appropriate to call it “Docet Classification System”.

Special Notice: According to the report, more than half of the plant species in Hong Kong are facing various threats caused by human activities, and some of them are even at risk of extinction. Kadoorie Farm and Botanic Garden (KFBG) has long been committed to the study and conservation of plant biodiversity in Hong Kong. The herbarium specimens and seeds collected by KFBG are used exclusively for scientific research, conservation and forest restoration, and the collection of these materials has been authorized by the Agriculture, Fisheries and Conservation Department (AFCD) of the Government of the Hong Kong Special Administrative Region (HKSAR). Collecting plant specimens and seeds in Hong Kong without permission of AFCD is a violation of the law.

Acknowledgements:
I would like to thank Ye Jianfei, Yang Tuo, Fiona Lo, Huiling Zhu, Stephan Gale, and Ann Williams for comments and suggestions.

Further reading
1. Angiosperm Phylogeny Group. (2016). An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV. Botanical Journal of the Linnean Society, 181(1), 1–20. https://doi.org/10.1111/boj.12385
2. Beentje, H. J. (2010). The Kew plant glossary: an illustrated dictionary of plant terms. Royal Botanic Gardens.
3. Bentham, G. (1861). Flora Hongkongensis: a description of the flowering plants and ferns of the island of Hongkong. London. L. Reeve.
4. Christenhusz, M. J., & Byng, J. W. (2016). The number of known plants species in the world and its annual increase. Phytotaxa, 261(3), 201-217.
5. Christenhusz, M. J., Reveal, J. L., Farjon, A., Gardner, M. F., Mill, R. R., & Chase, M. W. (2011). A new classification and linear sequence of extant gymnosperms. Phytotaxa, 19, 55-70.
6. Chun W., Y. (1953). New Species of Machilus from South China. Acta Phytotaxonomica Sinica. 2(3): 163-171. 
7. Dunn, S. T. , Tutcher, W. J.(1912). Flora of Kwangtung and Hongkong (China).  His Majesty’s Stationery Office, London. 
8. Gale, S. W., Kumar, P., Hu, A.-Q., & Pang, K. S. (2013). Cheirostylis pusilla (Orchidaceae), a new record for Hong Kong. Kew Bulletin, 68(2), 325–330. https://doi.org/10.1007/s12225-013-9437-1
9. Gale, S. W., Yeung, W. K., Ho, N., Chan, C. S., & Kumar, P. (2020). Four new additions and a taxonomic amendment to the orchid flora of Hong Kong. Taiwania, 65(4). https://doi.org/10.6165/tai.2020.65.575
10. Harris, J. G., & Harris, M. W. (1994). Plant identification terminology: an illustrated glossary. Utah: Spring Lake Publishing. 
11. Hu, A.-Q., Gale, S. W., Kumar, P., Fischer, G., & Pang, K. S. (2014). Taxonomic notes on Didymoplexiella siamensis and Gastrodia peichatieniana, two fully mycoheterotrophic orchids new to the flora of Hong Kong. Annales Botanici Fennici, 51(3), 177–184.
12. Kumar, P. (2023). Orchid Flora of Hong Kong: The addition of Crepidium bahanense. Rheedea, 33(3), 199–203. https://doi.org/10.22244/rheedea.2023.33.03.05
13. Kumar, P., & Gale, S. (2022). Taxonomic notes on Apostasia nipponica and Crepidium cordilabium (Orchidaceae), two species newly recorded from Hong Kong. Feddes Repertorium, https://doi.org/10.1002/fedr.202200002
14. Kumar, P., & Gale, S. W. (2020a). Additions to the orchid flora of Laos and taxonomic notes on orchids of the Indo-Burma region-II. Taiwania, 65(1), 47–60. https://doi.org/10.6165/tai.2020.65.47
15. Kumar, P., & Gale, S. W. (2020b). Anoectochilus formosanus (Orchidaceae), a new record for Hong Kong. Rheedea, 30(2), 293. https://doi.org/10.22244/rheedea.2020.30.02.06
16. Kumar, P., & Gale, S. W. (2023). Cheirostylis yunnanensis var. gloriae, an interesting new caterpillar orchid from Hong Kong, China. Feddes Repertorium. https://doi.org/10.1002/fedr.202200052
17. Kumar, P., Gale, S. W., Kocyan, A., Fischer, G. A., Averyanov, L., Borosova, R., Bhattacharjee, A., Li, J.-H., & Pang, K. S. (2014). Gastrochilus kadooriei (Orchidaceae), a new species from Hong Kong, with notes on allied taxa in section Microphyllae found in the region. Phytotaxa, 164(2), 91. https://doi.org/10.11646/phytotaxa.164.2.3
18. Le Bras, G., Pignal, M., Jeanson, M. L., Muller, S., Aupic, C., Carré, B., ... & Haevermans, T. (2017). The French Muséum national d'histoire naturelle vascular plant herbarium collection dataset. Scientific Data, 4(1), 1-16.
19. Lee, T., C., W., Chau, K., C, L., Wu S., H., (2003). Flora of Hong Kong: Pteridophyta. Hong Kong. Kadoorie Farm and Botanical Garden
20. PPG I. (2016). A community‐derived classification for extant lycophytes and ferns. Journal of Systematics and Evolution, 54(6), 563–603. https://doi.org/10.1111/jse.12229
21. Qian H., Zhang J., Zhao J. (2022). How many known vascular plant species are there in the world? An integration of multiple global plant databases. Biodiversity Science, 30(7): 22254.
22. Seemann, B. (1857). The botany of the voyage of HMS Herald: Under the command of Captain Henry Kellett, RN, CB, during the years 1845-51. Lovell Reeve.
23. Song, Z., Ye, W., Dong, S., Jin, Z., Zhong, X., Wang, Z., Zhang, B., Xu, Y., Chen, W., Li, S., Yao, G., Xu, Z., Liao, S., Tong, Y., Zeng, Y., Zeng, Y., Chen, Y. (2023). A dataset on inventory and geographical distributions of higher plants in Guangdong, China. Biodiversity Science, 31, 23177. DOI: 10.17520/biods.2023177.
24. Turland, N. J., Wiersema, J. H., Barrie, F. R., Greuter, W., Hawksworth, D. L., Herendeen, P. S., Knapp, S., Kusber, W.-H., Li, D.-Z., Marhold, K., May, T. W., McNeill, J., Monro, A. M., Prado, J., Price, M. J. & Smith, G. F. (eds.) 2018:  International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code)  adopted by the Nineteenth International Botanical Congress Shenzhen,  China, July 2017. Regnum Vegetabile 159. Glashütten: Koeltz Botanical Books. DOI https://doi.org/10.12705/Code.2018
25. Wang, G.-T., Shu, J.-P., Jiang, G.-B., Chen, Y.-Q., & Wang, R.-J. (2021). Morphology and molecules support the new monotypic genus Fenghwaia (Rhamnaceae) from south China. PhytoKeys, 171, 25–35. https://doi.org/10.3897/phytokeys.171.57277
26. Xing, F. W., Ng, S. C., & Chau, L. K. C. (2000). Gymnosperms and angiosperms of Hong Kong. Memoirs of the Hong Kong Natural History Society, 23, 21-135.
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Websites
1. Aiplants https://www.plantplus.cn/cn/tools/1 
2. Catalogue of Life China Annual Checklist http://www.sp2000.org.cn/ 
3. Check List of Hong Kong Plants 2012 https://www.herbarium.gov.hk/tc/publications/books/book5/index.html 
4. Chinese Field Museum https://cfh.ac.cn/ 
5. Chinese Virtual Herbarium https://www.cvh.ac.cn/ 
6. Digitising Kew's Collections https://www.kew.org/science/digitising-kews-collections
7. Docet Botanical Wiki https://duocet.ibiodiversity.net/ 
8. Flora of China http://www.efloras.org/flora_page.aspx?flora_id=2 
9. Flora of Guangdong http://fgd.scbg.ac.cn/ 
10. Flora of Hong Kong https://www.herbarium.gov.hk/sc/publications/books/book4/index.html 
11. Flora of Shenzhen https://www.iplant.cn/fsz/ 
12. Flora Reipublicae Popularis Sinicae https://www.iplant.cn/frps 
13. In the back, S.W. https://www.kfbg.org/en/departments/flora-conservation-department/Dr-Stephan-W-Gale
14. GBIF the Global Biodiversity Information Facility https://www.gbif.org/ 
15. HK Plant Database https://www.herbarium.gov.hk/tc/hk-plant-database/index.html 
16. HKCWW Plant Database http://hkcww.org/hkplant/index.php 
17. iNaturalist https://www.inaturalist.org/ 
18. Jstor Herbarium specimens https://plants.jstor.org/collection/TYPSPE 
19. National Specimen Information Infrastructure http://www.nsii.org.cn/2017/home.php 
20. Plant Science Data Center https://www.plantplus.cn/cn 
21. Plant Search Engine at the Initiative for Collective Conservation in Chinese Botanical Gardens https://image.cubg.cn/ 
22. PlantNet https://identify.plantnet.org/zh-hant 
23. Plants of the World Online https://powo.science.kew.org/ 
24. Saunders R.M.K. https://www.ipni.org/a/36518-1 
25. World Flora Online (WFO) https://www.worldfloraonline.org/ 
26. Xingse https://www.xingse.net/