How to Identify Orchid Roots? A Practical Guide to Identification Methods

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The roots of Cymbidium plants are relatively thick and fleshy. Generally, there is no distinction between a main root and branch roots.

The internal structure of orchid roots is of the typical monocotyledonous type. Its cortical cells are relatively well developed, with symbiotic fungi known as mycorrhizae. Roots growing underground are called terrestrial roots, while those growing in the air are called aerial roots. Whether terrestrial or aerial, 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 elongated cylindrical and polygonal, arranged radially from the center outward.

When the velamen cells mature, the protoplasm disintegrates and thickened stripes form 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 within the cortex.

The middle layer of the orchid root is the cortical tissue, whose cells are relatively well developed, about 20 layers of polygonal cells, about 3 times the thickness of the velamen tissue, and making up most of the root. The outermost layer, adjacent to the velamen tissue, is the exodermis, which consists of a single layer of cells arranged radially, neatly, and larger in volume than ordinary velamen cells; inside it is the cortex, and some cortical cells contain needle-shaped crystals, some contain chloroplasts, and some contain symbiotic mycorrhizae.

The inner layer of the orchid root is the central cylinder. The outermost layer of the central cylinder, where it meets the cortex, is the endodermis, and the Casparian strips on the endodermal cells are well developed. Closely attached to 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. Those on the outer periphery of the phloem are sclerenchyma cells; those on the outer periphery of 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. The orchid root has numerous vascular bundles, whose xylem and phloem are separate and arranged radially. Around the xylem and phloem there is fibrous tissue forming a tube column; at the center is the pith of thin-walled cells.

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

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