The genus Cinnamomum

54 P.N. Ravindran et al.
Pericarp: The pericarp consists of the following tissues: (i) a sclerenchymatous
epicarp the cells of which have thick outer walls and thin inner walls; (ii) a mesocarp of
stone cells, parenchyma cells, secretion cells and vascular tissue. Stone cells vary in size
and shape and they underlie the epicarp. Parenchyma cells occupy the major portion of
the mesocarp. Cell contents vary in colour from light to dark brown. Secretion cells are
numerous, calcium oxalate crystals present; (iii) an endocarp of sclerenchymatous tissue
except in the basal region of the fruit, where it is parenchymatous.
Seed coat: The seed coat consists of the following regions: (i) an outer tissue of four
to six layers of deeply pigmented (dark brown) parenchyma cells. These cells are
tangentially elongated to about 90 ; (ii) an almost complete tissue of reticulated cells.
In the upper part of the seed these cells are arranged in palisade fashion, the innermost
cells being the longest (about 100 ). Reticulated cells are not evident in the basal
region; and (iii) an incomplete parenchymatous tissue underlying the reticulate cells,
five to six layers and irregular in shape. Calcium oxalate crystals are present in the cells.
Pedicel: In CS the pedicel consists of the following parts: (i) epidermis – epidermal
cells are small and rectangular cells with thick outer walls; (ii) cortex – consists of
isodiametric, thin walled parenchyma cells with dark contents, secretion cells and occasional
stone cells; (iii) pericycle – marked by an almost continuous ring of thick walled
fibres; (iv) an almost complete ring of fibrovascular tissue; and (v) a pith of isodiametric
parenchyma cells.
Biosystematics and inter-relationships
Shylaja (1984), Shylaja and Manilal (1998) and Ravindran et al. (1991, 1996) carried
out numerical taxonomic studies on C. verum and some of the related taxa. Cluster
analysis of characters led to the clustering of the following characters: (i) bud type,
stomatal type, phyllotaxy and epidermal thickness; (ii) hairiness, hair frequency and
hair length; (iii) inflorescence length, nature and type; (iv) thickness of leaf, palisade
and spongy parenchyma; and (v) leaf length and leaf breadth. The first three sets
of characteristics are important for taxonomic delimitation of taxa. Cluster analysis of
taxa using centroid linkage led to the grouping of C. verum with some collections
of C. malabatrum, while C. cassia and C. camphora formed unique groups. Much variability
exists in C. malabatrum, in which some of the collections clustered with C. verum, while
others formed eight distinct groups. This result led to a re-examination of the C. malabatrum
complex from which one new species and one variety were identified (Shylaja,
1984; Manilal and Shylaja, 1986). In fact, the malabatrum complex requires a closer
study. Principal component (PC) analysis (Shylaja, 1984; Ravindran et al., 1996) was
used to analyse the characteristics responsible for species divergence. The dispersion of
OTUs between the PCs shows that C. camphora gets diverged from other species due to
the first PC (bud type, stomatal type, phyllotaxy, epidermal thickness). The second PC
(hairiness, hair size, and hair frequency) is responsible for the divergence of C. perrottettii,
C. riparium and C. macrocarpum. C. cassia diverges from the rest of the species by the
third PC (inflorescence length, nature and type). The fourth PC (thickness of leaf,
palisade and spongy parenchyma) and fifth PC (leaf length and leaf breadth) are responsible
for the divergence of various C. malabatrum collections. Species such as C. camphora,
C. cassia, C. riparium, C. macrocarpum and C. perrottettii remain independent entities with
respect to the PCs studied, thereby indicating their taxonomic independence. C. verum
and C. malabatrum show considerable closeness, indicating their taxonomic affinity.