Classification and Taxonomy

The Importance of Botanical Names

Have you ever wondered why botanical or scientific names are so crucial? Much like specific co-ordinates or postal codes, botanical names—also known as binomial nomenclature—are essential for uniquely identifying plants. This system uses two names: the genus and the species. For instance, Taraxacum officinale denotes the common dandelion. This universal naming system transcends language barriers, ensuring that a particular plant is easily identifiable regardless of where you are or what language you speak.

In contrast, common names can vary widely across different regions and cultures, leading to significant confusion. For example, the White Waterlily (Nymphaea alba) has 15 different common names in English alone, and over 240 names in other languages. Similarly, the term "pepper" can refer to various plants. Bell peppers, which are not spicy and come in various colours such as green, red, yellow, and orange, belong to Capsicum annuum. In contrast, the pepper used as a seasoning is from Piper nigrum. Additionally, chilli peppers are another variety of Capsicum. This demonstrates the potential for confusion when relying solely on common names.

The need for classification

The sheer number of plant species is immense. Scientists estimate there are approximately 300,000 plant species, and when including fungi, moulds, mushrooms, and toadstools, the total rises to around 450,000. Despite this, we still have much to learn about the world’s plants. Estimates suggest that 15-20% of plant species have not yet been described, and approximately 2,000 new plant species are discovered annually. With over 14 million living species on Earth, only 1.8 million have been given botanical names.

The Linnaean classification system helps us to organise plants and animals, aiding in the understanding of biological evolution. This vast and diverse plant kingdom necessitates a structured classification system, particularly in industries like horticulture, where plants are encountered daily.

Classification serves as an efficient means of reference and communication. A plant’s name must be unambiguous to prevent miscommunication. If a plant is known by different names to different people, it can lead to confusion and ineffective communication.

The ICBN and ICNCP

The International Code of Botanical Nomenclature (ICBN) governs the formal naming of plants, ensuring that each taxonomic group, or 'taxa,' has only one globally accepted name. When a new plant is discovered, it is given a botanical name and formally described according to international regulations. A recent innovation in the ICBN is the introduction of the ‘Standard Specimen,’ a voucher specimen stored in a herbarium to aid in identifying new cultivars.

The ICBN ensures that plant names are appropriately assigned and prevents the confusion that could arise from inconsistent naming. Without such a system, plants might receive incorrect names, destabilising the taxonomic groups and causing ambiguity in the scientific community. For example, the genus Andrographis echioides was moved to a new genus Neesiella by Sreemandhaven in 1967, but since the name Neesiella was already used for another genus, this change was deemed illegitimate. Sreemandhaven later revised the name to Indoneesiella.

However, frequent updates to the ICBN have sometimes led to disputes among plant scientists and horticulturists. Changes in classification can stem from advances in scientific knowledge or deviations from the code’s provisions, ironically causing instability despite the code’s intent to standardise naming.

The International Code of Nomenclature for Cultivated Plants (ICNCP) addresses the naming of 'cultigens'—plants created or modified by human activity. This includes cultivars and groups. Examples regulated by the ICNCP include Clematis alpina 'Ruby' (a cultivar), Magnolia 'Elizabeth' (a hybrid), Rhododendron boothii Mishmiense Group (a group name), and Apple 'Jonathan' (a cultivar).

The ICNCP’s development began in 1862 with Alphonse de Candolle’s proposal, leading to the establishment of a temporary code and subsequent revisions until the formation of the ICNCP in 1952. This code ensures clarity and consistency in cultivar names used commercially and scientifically.

Plant classification

Plants, like all organisms, are classified in a hierarchical system that reflects evolutionary relationships. Taxonomists, such as Linnaeus, work to place organisms within an evolutionary framework. Organisms are classified into five kingdoms: Animalia (animals), Plantae (plants and some multicellular algae), Fungi (fungi), Monera (prokaryotic bacteria), and Protista (eukaryotic microorganisms and algae). These kingdoms represent the most ancient branches of life’s evolutionary tree, with substantial evolutionary gaps between them.

Historically, organisms were grouped into two kingdoms: Fauna (finite growth, movement, and consumption) and Plantae (indefinite growth, immobility, and non-consumption). As science progressed, it became clear that this approach was inadequate. For instance, lichens, once classified under Plantae, are now understood to be symbiotic partnerships between fungi and algae. This complex relationship led to lichens being classified under Fungi, though this classification remains contentious.

The classification system within each kingdom further divides organisms into phyla (or divisions), classes, orders, families, genera, and species. The Plantae kingdom, for example, includes various phyla such as Bryophyta (mosses and liverworts), Pteridophyta (ferns), Gymnospermae (conifers), and Magnoliophyta (flowering plants). Within each phylum, organisms are organised into classes, orders, families, and genera, each representing increasingly specific groupings.

The genus represents the closest relationship among organisms, with species being the smallest unit. For example, within the genus Rosa, species include Rosa acicularis and Rosa nutkatensis. The binomial naming system, pioneered by Linnaeus, provides a two-term designation that facilitates global communication.

Despite its utility, the classification system faces challenges and is in constant flux. Disputes over taxonomic placement, such as the classification of lichens and algae, illustrate the complexity of accurately categorising diverse life forms.

Defining a species

At the lowest level of classification is the species, a concept still not fully understood. Traditionally, a species is defined as a group of similar individuals that can reproduce successfully among themselves while remaining reproductively isolated from other species. However, the evolutionary continuum and the vast range of variation make this definition challenging.

The Phylogenetic Species Concept, which focuses on evolutionary history and genetic differences, offers an alternative view. This concept can lead to recognising a greater number of species compared to the Biological Species Concept. Combining both systems may provide a more comprehensive understanding of species.

Infraspecific or subspecific taxonomy helps to account for variation within species. Populations nearing species status are often classified as subspecies or varieties, such as Salix reticulata ssp. reticulata and S. reticulata ssp. glabellicarpa. This approach allows scientists to catalogue and name variations within a species.

In summary, taxonomy is essential for classifying organisms based on structural similarities and evolutionary relationships. The vast diversity of plant species and the continual discovery of new ones highlight the need for a systematic classification system. Linnaeus’s binomial nomenclature remains a cornerstone of this system, aiding global understanding and communication. The ICBN and ICNCP regulate plant names to maintain consistency and clarity in both scientific and commercial contexts.