Leaf morpho-anatomy and taxonomic significance in six Phalaenopsis s. l. (Orchidaceae) species from China

Phalaenopsis is well-known as a highly ornamental and rare orchid. The taxonomy and infrageneric relationship of the genus of Phalaenopsis s. l. has been highly disputed due to some overlapping morphological features. Leaf morpho-anatomy of six Phalaenopsis s. l. species from China were investigated using a microscope and paraffin section to provide new evidence for taxonomic implications. The observation of the study revealed the following: (1) The shape of the ordinary epidermal cells on both sides are polygonal with straight-arched anticlinal wall. (2) Papillae occurre on each epidermal cells and are present on both leaf sides, including the uni-papilla on both the adaxial and abaxial epidermis cells in these six species, with an exception of the bi-papillae on adaxial epidermis cells in P. wilsonii and P. braceana. (3) Orbicular stomata and elliptic stomata occur only on the abaxial epidermis, commonly with co-occurrence of tetracytic and anomocytic stomata. (4) The straight type and the convex type of outline of leaf midrib were observed in six Phalaenopsis s. l. species. The thickness of leaf midrib is different greatly, the thickest observed in P. deliciosa and the thinnest observed in P. braceana. (5) Spherical silica bodies and prismatic and raphide crystals were observed in six Phalaenopsis s. l. species. Some leaf morpho-anatomic features were selected and used for species discrimination, including the size of ordinary epidermal cells, type of papillae, stomatal shape and density, thickness and outline of cross-section of a leaf midrib, and crystal type. Meanwhile, it was supported that Kingidium should be grouped into Phalaenopsis s. l., since P. deliciosa (syn. = K. deliciosum) and P. braceana (syn. = K. braceanum) shared common leaf morpho-anatomic features with the other four species of Phalaenopsis s. s. In addition, a key to six Phalaenopsis s. l. species from China was proposed based on leaf morpho-anatomic features.