An Herbiary of Plant Individuality

Abstract

Questioning the nature of individuality has a long and a rich history, both in philosophy and in biology. Because they differ in several features from the pervasive vertebrate-human model, plants have been considered as complicating the question. Here, the various plant species on which authors-whether biologists or philosophers-rely to build the picture of plant individuality are examined and tracked for their peculiarities, thus constituting an "herbiary" of plant individuality. The herbiary of plant individuality has as its members species exhibiting a diverse collection of traits and illustrating different questions related to plant individuality. This essay assesses the peculiarity of the features of these plants and the reality of their differences from animals. Because some plant features are supposed to pose a threat to individual genetic homogeneity, higher heterogeneity has been assumed for plants compared to animals. Moreover, individual plants are sometimes identified with communities. How does this supposed heterogeneity appear in particular species? Cultivated plants exhibit distinctive diversity, and their overrepresentation in the study of plant diversity might bias the way plant individuality is understood. Just as there is a vertebrate bias, there may also be a cultivated plant bias. Recent results bring plants much closer to animals in terms of cellular functioning, so plants might not be so different from animals with respect to their diversity, and consequently their individuality.

Oak symbolism in the light of genomics

“…These findings challenge the poetic vision of each tree as a forest in its own right (Hallé, ). After a detailed analysis at the interface between population genetics and philosophy, Gerber () reached a similar conclusion. These findings suggest that taller plants may have low rates of mutation per unit time, consistent with the conclusions of Lanfear et al .…”

Lifetime genealogical divergence within plants leads to epigenetic mosaicism in the long-lived shrubLavandula latifolia(Lamiaceae)

“…Modular construction by continual organogenesis and reiterated production of homologous structures is a quintessential plant feature which has motivated the consideration of plant individuals as non-unitary metapopulations of semi-autonomous modules, a notion departing from the common zoocentric definition of organismic individuality (Gerber, 2018). This view led to the incorporation of selection at the subindividual level as a possible evolutionary mechanism (Buss, 1983a, b; Pineda-Krch & Poore, 2004), and provided the foundations for the ‘genetic mosaicism hypothesis’ (GMH) (Whitham & Slobodchikoff, 1981; Whitham et al ., 1984; Gill et al ., 1995).…”

“…The phenotypic effects of these polymorphisms, however, have been investigated on few occasions. Genetic heterogeneity caused by somatic mutations is unlikely to be a pervasive driver of within-plant heterogeneity in wild plants, given the paucity of well-documented genetic mosaics and the extremely low somatic mutation rates reported whenever such mosaics have been found (Padovan et al ., 2013; Ranade et al ., 2015; Schmid-Siegert et al ., 2017; Gerber, 2018; Wang et al ., 2019; Orr et al ., 2020). Somatic mutations altering nuclear or plastid DNA sequences are not, however, the only molecular mechanism with a capacity to produce genomic heterogeneity and induce phenotypic variation within individual plants.…”

Can't see the colony for the bees: behavioural perspectives of biological individuality

“…The ability to separate Physarum into multiple individuals is analogous to the way cuttings from plants can take root and create new individuals. The modular nature of plants – the fact they can often be separated into smaller sections, like branches and roots, which are self‐reproducing and semi‐autonomous (De Kroon et al ., ; Herrera, ; Gerber, ) – is also similar to the growth of plasmodial slime moulds, and creates interesting questions around the different environmental conditions two ‘modules’ might face, and how this affects organismal fitness. Indeed, the individuality question as applied to plants is historically complicated, particularly in an evolutionary context (Tuomi & Vuorisalo, ; Clarke, ), but also in ecological research when for example one needs to estimate population size.…”

“…Evidence for inter‐clonal variation in morphological and physical traits in pine trees ( Pinus pinea ) suggests the answer will be ‘yes’ (Sánchez‐Gómez et al ., ). Monozygotic twins also suggest such an answer (Bruder et al ., ; Li et al ., ), although the analogy to plants is complicated by the segregation of germline and soma in animals (Gerber, ; see Lanfear, for an interesting discussion of germ–soma segregation in plants).…”