Morphological knowledge in plant ecology and why it matters

Plant form has been used as a surrogate for studying function from the beginning of the field of plant ecology (Warming, 1909) in multiple approaches, including comparative morphology, growth form and life-form classifications, and plant architecture. Nevertheless, with new methods to directly measure functions such as photosynthesis and an increasing focus on large-scale studies and large data sets, a full consideration of morphology (form) may appear old-fashioned. Still, one branch of plant ecology, trait-based ecology, studies how morphology relates to functions.

Indeed, trait-based ecology, a subdiscipline that has been developing for several decades (Westoby, 1998), uses well-defined morphological or anatomical traits as a proxy for function (Box 1). It represents a culmination of efforts to understand plant strategies using morphological characters, which began with the work of von Humboldt (1807), and continued through numerous classifications of growth or life forms (e.g., Raunkiaer, 1907). Finally, at the end of the 20th century, elaborate morphological classifications were replaced by a few plant traits that were easy to measure and collect data that could be analyzed statistically (Westoby, 1998; Weiher et al., 1999).

The focus on plant functional traits accelerated this discipline by enabling formalized approaches that could be applied over large scales and ecosystems (Díaz et al., 2016). A few of the traits commonly used for this purpose include acquisitive traits of leaves (e.g., leaf thickness, specific leaf area) and the plant's ability to overtop other plants and acquire aboveground resources (plant height) and to disperse and provision progeny (e.g., seed size) (Westoby, 1998). Acquisitive traits of fine roots have also been added to this portfolio (Bergmann et al., 2020). The ease of data collection for these traits according to standard protocols (Perez-Harguindeguy et al., 2013) has resulted in the assembly of trait values in freely accessible databases (e.g., Kattge et al., 2020) and in the widespread use of functional traits in many ecological disciplines (e.g., invasion ecology, restoration ecology; Westoby, 2025), without directly studying the functions of these traits in an ecological context.

After a quarter century of functional ecology research, we can see some consequences of the restricted focus on a few easily measurable traits that make broad comparisons across ecosystems or continents possible, but that are free from the “burden” of dealing with the diversity of whole-plant growth forms. This reductionistic approach, which has facilitated unprecedented, large synthetic studies of plant form and function in response to challenges of resource availability (Díaz et al., 2016; Bergmann et al., 2020), has at the same time side-lined functionally relevant information that requires morphological knowledge that is not captured by the measurement of the widely adopted traits noted above, such as specific leaf area or plant height. This absence of a broader spectrum of morphological data has likely substantially hindered understanding of plant function in situations in which resource availability fluctuates over time due to seasonality or disturbance, i.e., in nearly all biomes on Earth.

With only acquisitive traits in mind, scientists can miss the fact that plants not only forage for and acquire resources, but that they may also store them for future use, which is a necessary condition for survival when resource availability fluctuates over time. To store resources, plants generally use specific storage organs, whose function and functional limitations cannot be fully understood without using a morphological approach. Resource storage is a prerequisite for survival in recurrently disturbed habitats (Pausas et al., 2018), and in seasonal climates, storage is also important for resuming growth after dormancy and for the timing of growth and flowering (Harris et al., 2025). Moreover, the location of storage in turn affects morphology and growth form in ways that also have functional consequences (Bellingham and Sparrow, 2000).

Although the inclusion of storage as a trait in functional ecology approaches might seem to be an easy solution, delimiting what is considered as a plant storage organ and identifying which variable of an organ is best to measure (Box 1) are not trivial tasks. The necessary standardization is complex: Organs for storage may have diverse morphological composition and be built of leaves, stems, or roots or different combinations of these organs. In the botanical literature, there is also enormous heterogeneity in the terminology surrounding storage organs, with different meanings for the same term used in different regions (e.g., multiple definitions of the term rootstock; see Beentje, 2010)—or use of an ecosystem-specific vocabulary (for example, compare Pausas et al., 2018 and Klimešová and Herben, 2024). This situation makes standardization difficult across methods and limits mutual understanding among researchers. Storage organs and resource storage are but one example where functional ecology fails to include important plant traits due to its focus largely on leaves and fine roots. Other examples of this issue include clonal growth organs and clonal multiplication as well as the bud bank and resprouting. All of these have important ecological functions, particularly related to the plant's ability to access a volume of soil and to respond to disturbance (Klimešová et al., 2018).

One solution to the challenge of encompassing an expanded array of morphological or developmental traits may lie in defining functions and relevant traits not for individual morphologically defined organs but for any organ providing such functions. For example, clonal spread and multiplication is realized through the growth of specialized organs such as rhizomes, stolons, bulbs, or roots with adventitious sprouting. We can therefore define and standardize measurements for all clonal growth organs together and study clonal growth strategies across all organ types that provide plants with the ability to reproduce or spread clonally (e.g., Chelli et al., 2024). Nevertheless, detailed analyses based on morphological knowledge of clonal growth organs (for example, the ability to distinguish among rhizomes, stolons, bulbs, roots with adventitious sprouting, and so on) substantially improves our understanding of the role that clonal growth plays in affecting the distribution of plants along environmental gradients (Klimešová and Herben, 2024)—and such detailed analysis relies on defining organs according to morphological origin.

Alas, we have little opportunity to identify how ignoring complex, usually belowground storage and clonal growth organs, may affect our understanding of plant function and its evolutionary development because large-scale, reliable morphological data are not readily available. We can potentially expand the number of plant species for which trait values are at our disposal by using procedures such as text mining of taxonomic descriptions (e.g., Folk et al., 2024). This approach, however, is not ideal because the taxonomic descriptions of belowground organs use a taxon-specific terminology and/or may not even exist in the literature, when not necessary for plant determination or species delimitation (Figure 1). Combining the effort of ecologists and taxonomists in description of taxa, following agreed standard protocols including unified terminology could be an efficient response to this issue, as could collation of existing data, with targeted data collection on belowground morphology in taxonomic groups where data are missing.

The inclusion of morphological knowledge in ecological studies does not necessarily mean only using more morphological categories—either for organs or growth forms. It may mean including analyses of architectural variables, such as branching patterns or reiteration of plant modules (Laurans et al., 2024). We argue that ecology would benefit from including basic morphological knowledge in its portfolio. The easiest step is to ask ecology lecturers to pay greater attention to the fundamentals of plant morphology when preparing lessons that address organ functioning and functional traits or by adopting practical courses or course modules that allow students to observe and experience the morphology of the whole plant body. The latter should include organs that are not acquisitive but may be hidden in the soil. Comparative morphologists, functional morphologists, and anatomists could also be invited to participate in organizing or providing content in ecology summer schools (for example) and to provide online or in-person resources for teaching and learning. There should also be increased sharing of training and course and curriculum development between plant ecologists and plant taxonomists. We believe that a deeper knowledge of morphology would also avoid reanimating old and pedantic discussions on morphological terminology in ecology, which should instead focus on understanding the evolutionary and developmental constraints on plant ecological function.

J.K. conceived the idea, and all authors further developed the idea and contributed to writing the essay.