How to Identify Orchid Roots? A Few Practical Identification Methods

The roots of orchids in the genus Cymbidium are relatively thick and fleshy. Generally, there is no distinction between a main root and lateral roots.

     The internal structure of orchid roots is a typical monocotyledonous type. Its cortical cells are relatively well developed, and it has symbiotic fungi called root fungi. Those growing underground are called terrestrial roots, and those growing in the air are called aerial roots. Whether terrestrial roots or aerial roots, their internal structure is basically the same and can be divided into an outer layer, a middle layer and an inner layer.

     The outermost layer is the velamen tissue, which originates from the epidermal tissue. The cells of the velamen tissue are long cylindrical and polygonal, arranged radially from the center outward. When the velamen cells mature, the protoplasm disintegrates and thickened stripes develop on the cells. The function of the velamen tissue is to protect the cortex, absorb water, and reduce and protect against the loss of water from inside the cortex.

     The middle layer of the orchid root is the cortical tissue. The cells are relatively well developed, about 20 layers of polygonal cells, about 3 times the thickness of the velamen tissue, and make up most of the root. The outermost layer, closely adjoining the velamen tissue, is the exodermis. It is composed of a single layer of cells, arranged radially and neatly, and larger in size than ordinary velamen cells; inside it is the cortex. Some cortical cells contain needle-shaped crystals, some contain chloroplasts, and some contain symbiotic root fungi.

     The inner layer of the orchid root is the central cylinder. The outermost layer of the central cylinder, where it connects with the cortex, is the endodermis, and the Casparian strips on the endodermal cells are very well developed. Closely adjoining the endodermis is a layer of vascular bundle sheath. Both the endodermis and the vascular bundle sheath have two types of cells with different structures. Around the phloem are sclerenchyma cells; around the xylem are parenchyma cells. The sclerenchyma cells mainly strengthen the root, while the parenchyma cells are conducting tissue used to transport water and nutrients. Orchid roots have many vascular bundles, and their xylem and phloem are separate and arranged radially. Around the xylem and phloem there is fibrous tissue, forming the vascular column; the center is the pith of thin-walled cells.

    Most epiphytic orchids, in addition to underground roots, also have many aerial roots. The functions of aerial roots, in addition to absorption, fixation and protection, include the parts with chlorophyll, which can also carry out photosynthesis and make food.