Linnaea

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Credits

Tom Christian (2021)

Recommended citation
Christian, T. (2021), 'Linnaea' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/linnaea/). Accessed 2021-05-09.

Family

  • Caprifoliaceae

Species in genus

Glossary

section
(sect.) Subdivision of a genus.
family
A group of genera more closely related to each other than to genera in other families. Names of families are identified by the suffix ‘-aceae’ (e.g. Myrtaceae) with a few traditional exceptions (e.g. Leguminosae).
monograph
Taxonomic account of a single genus or family.
monophyletic
(of a group of taxa) With a single ancestor; part of a natural lineage believed to reflect evolutionary relationships accurately (n. monophyly). (Cf. paraphyly polyphyly.)
monospecific
(of a genus) Including only one species (as e.g. Aextoxicon).
polyphyletic
(of a taxon) Including entities descended from different ancestors and evolutionary lineages grouped usually as a result of superficial similarities (n. polyphyly). The grouping is therefore not ‘natural’. (Cf. monophyly paraphyly.)
sensu lato
(s.l.) In the broad sense.

Credits

Tom Christian (2021)

Recommended citation
Christian, T. (2021), 'Linnaea' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/linnaea/). Accessed 2021-05-09.

Treated here in the traditional sense, as a monospecific genus of circumboreal distribution. See discussion of alternative applications below; for the botanical description see L. borealis.

In the traditional sense, Linnaea is a genus of a single diminutive species with a circumboreal distribution in the north northern hemisphere (Cullen et al. 2011). In has traditionally been placed in the Honeysuckle family, the Caprifoliaceae. This family is home to several horticulturally important genera including Abelia, Lonicera, Symphoricarpos, and Weigela; consequently it has been much studied and subject to considerable (proposed) reorganisation.

In recent years molecular phylogenetic studies have shown the well-known genus Abelia to be polyphyletic. In order to achieve monophyly – a tenet of modern botany – authors including Landrein et al. (2012) have resurrected older names to accommodate sections of Abelia sensu lato, including Vesalea for those species distributed primarily in Mexico, and Zabelia for a number of the Asiatic species; several more including the type, A. chinensis, remain in a much-reduced Abelia, and a new genus, Diabelia, was described in 2010 to accommodate the rest (Christenhusz 2013; Landrein 2010). Each of these genera contains only a small number of species – Abelia itself is reduced to just five species in this treatment. Christenhusz (2013) pointed out this wasn’t concordant with approaches to other subfamilies within the Caprifoliaceae, and expanded Linnaea in order to provide an alternative approach whilst still maintaining monophyly. In so doing he sinks the horticulturally significant Abelia (excluding Zabelia), Dipelta, and Kolkwitzia into a much-enlarged Linnaea. The nomenclatural ramifications of these changes are not excessive; the revised Linnaea amounts to only 16 species (15 new combinations; with 9 Abelia species previously treated in Section Zabelia now treated as species of Zabelia, itself restored to generic rank) (Christenhusz 2013).

As Christenhusz points out ‘…the delimitation of genera is arbitrary, and depends on tradition and preference of the user. Here, I am merely making the names available to provide a choice’ (Christenhusz 2013). This choice now available to authors is reflected in a range of approaches in major works. Plants of the World Online (plantsoftheworldonline.org) has adopted Christenhusz’s system, whereas others, for example the Catalogue of Life (catalogueoflife.org) have not. The Flora of China, where many of the groups in question have a significant distribution, has opted to retain separate genera following Landrein et al. 2012, necessarily invoking the segregation of Abelia, and goes further by placing them into the family Linnaeaceae (Yang & Landrein 2011). A recent publication from the Royal Botanic Gardens, Kew – A monograph of Caprifoliaceae: Linnaeeae – has also maintained separate genera (Landrein & Farjon 2020).

One of the principal arguments against accepting an enlarged Linnaea is the loss or partial loss of several genera well known in horticulture (Abelia, Dipelta, Kolkwitzia) and the ensuing nomenclatural turmoil that so often pits horticulturist against botanist. In this case, however, the status quo has been shown to be untenable due to the polyphyly of Abelia (sensu lato). The near-universal agreement that genera must be monophyletic demands either the broadening of Linnaea, or else the splitting of Abelia; either way, nomenclatural turmoil is unavoidable. For Trees and Shrubs Online we have opted to split Abelia in concordance with the Flora of China and the new publication A monograph of Caprifoliaceae: Linnaeeae (Landrein & Farjon 2020). It seems far preferable to retain the familiar names Dipelta and Kolkwitzia, and Abelia in a reduced sense, rather than lump all these together in a single genus, Linnaea, hitherto well-known as a monospecific, circumboreal subshrub of understated charm.