Abstract
In this study, we sampled 48 species of Asian Cinnamomum covering the species groups that were identified in recent phylogenetic studies and conducted leaf micromorphological observations using both light microscopy (LM) and scanning electron microscopy (SEM). Synapomorphies were determined by means of mapping micromorphological characters on a phylogenetic tree. The results indicate that Cinnamomum exhibits two different types of leaf upper epidermis: Type I has smooth/non-reticulate periclinal walls whereas Type II has reticulate periclinal walls and is unusual in the family Lauraceae. We found that the two types of micromorphological characters are clade-specific, sect. Camphora s.s. possesses Type I leaf upper epidermis, and sect. Cinnamomum s.l. has Type II leaf upper epidermis. Our study also reveals that C.saxatile, a member of sect. Camphora s.l. in the traditional classification, actually has Type II leaf upper epidermis, thus reinforcing the result of a recent molecular phylogeny that has this species in a clade consisting mainly of species of sect. Cinnamomum.
Highlights
The results indicate that Cinnamomum exhibits two different types of leaf upper epidermis: Type I has smooth/non-reticulate periclinal walls whereas Type II has reticulate periclinal walls and is unusual in the family Lauraceae
The upper leaf epidermal micromorphology of Asian Cinnamomum species falls clearly into two types according to the reticulation of the periclinal walls of leaf upper epidermis, cell shape and straightness of anticlinal walls
Our sampled species largely overlapped with the species sampling of the two recent molecular phylogenetic studies (Huang et al 2016; Rohde et al 2017), permitting an assessment of the systematic significance of leaf epidermal micromorphology within a phylogenetic context
Summary
In the family Lauraceae, there are some named generic complexes according to molecular systematic studies, e.g. the Beilschmiedia group, the Persea group, the Litsea group, the Alseodaphne group, and the Cinnamomum group (e.g. Chanderbali et al 2001; Rohwer et al 2009, 2014; Huang et al 2016; Trofimov et al 2016, 2019; Mo et al 2017; Rohde et al 2017; Trofimov and Rohwer 2020; Xiao et al 2020; Liu et al 2021). Phylogenetic studies based on DNA sequences suggest that Lindera is polyphyletic, and comprises many different clades (Li et al 2004; Fijridiyanto and Murakami 2009). How these clades can be recognized using morphological characters has become an important question in the taxonomy of the group. The group belongs to the Laureae-Cinnamomeae clade of the core Lauraceae (Chanderbali et al 2001; Rohwer and Rudolph 2005; Song et al 2017, 2020), and consists of several closely related genera, i.e. Cinnamomum Schaeff., Aiouea Aubl. The group is thought to have originated ca. 55 mya and was once widely distributed in the palaeotropical Arcto-Tertiary flora of Laurasia during the Eocene, migrated southwards and, with cooling temperatures, split, resulting in the modern amphi-Pacific disjunct distribution (Huang et al 2016)
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