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It is often surprising to realize that in many plant species, over half of the entire plant structure remains completely hidden beneath the soil surface. While common intuition suggests that roots are the sole organs existing underground, botanical studies reveal a diverse array of subterranean plant structures that serve critical survival functions.
These hidden structures are primarily categorized into two distinct types: roots and underground stems. Each type exhibits unique anatomical features, developmental origins, and physiological roles that enable plants to thrive in their specific environments, withstand unfavorable weather conditions, and store vital nutrients.
Understanding the morphological and anatomical characteristics of these underground plant organs is essential in pharmaceutical botany, as many medicinal drugs, therapeutic extracts, and commercial plant products are derived directly from roots, rhizomes, tubers, bulbs, and corms.
In vascular plants, the root is the specialized plant organ that typically and generally lies below the surface of the ground. Botanically referred to as radix (plural radixes or radices), roots play a fundamental mechanical role by anchoring the plant firmly in the soil and holding it in an upright position against environmental stresses like wind and heavy rain.
Beyond structural support, roots act as the primary physiological gateway for water and essential mineral absorption from the surrounding soil matrix. Once absorbed, these vital fluids and nutrients are conducted upward through the vascular system to the stems and leaves for photosynthesis and metabolism.
Furthermore, many roots serve as specialized storage organs for accumulating reserve food materials, such as carbohydrates and starches, which the plant can utilize during periods of dormancy, winter survival, or regenerative growth phases.
In numerous herbaceous plant species, specialized subterranean stems develop beneath the soil surface, functioning quite differently from typical aerial stems. These underground stems remain completely dormant during unfavorable environmental conditions, such as extreme cold or drought, and give rise to fresh green shoots as soon as favorable conditions return.
Underground stems generally function as major storage reservoirs for food, becoming swollen and fleshy to accumulate nutrients. They perform three core biological functions: the storage of food reserves, perennation to survive from one growing season to the next with periods of reduced growth, and vegetative propagation.
Vegetative propagation through underground stems represents a form of asexual reproduction where only a single parent plant is involved, resulting in genetically identical offspring. Structurally, underground stems can be differentiated from true roots by their stem-like internal anatomy, external branching patterns, and the distinct presence of nodes.
The first major type of underground stem is the rhizome (plural rhizomas or rhizomata), which is a horizontal subterranean stem capable of sending out both aerial shoots above and roots below. Rhizomes often become thickened to store food reserves and serve dual roles as both storage and reproductive structures.
A bulb is another specialized underground stem characterized by fleshy, scale-like leaves surrounding a central flower bud. Structurally, a bulb functions as a short stem with leaf bases acting as food storage organs during dormancy, protected externally by a papery covering known as a tunic that prevents physical damage and moisture loss.
Tubers represent enlarged, fleshy underground stems found in certain seed plants, uniquely featuring buds commonly referred to as 'eyes'. Under favorable conditions, these eyes produce aerial shoots to assist in vegetative propagation; importantly, tubers lack true roots, distinguishing them from rhizomes.
Finally, a corm (also called a bulbotuber) is a solid, swollen underground stem covered with dry, scale-like leaves, serving as an overwintering and drought-survival organ. Unlike bulbs, corms lack fleshy scales, bear multiple buds in the axils of their scale leaves to produce daughter corms, and develop adventitious roots from their bases or sides.
In pharmaceutical botany practical sessions, examining plant tissues requires precise microscopic work involving both cross-sectioning and powdered drug analysis. Students perform schematical and anatomical drawings using specialized investigation mediums such as SARTUR or distilled water, viewed under specific microscope magnifications like 10x4 or 10x40.
For instance, Glycyrrhiza glabra (liquorice or meyan) is analyzed in both cross-section and powdered drug form using SARTUR medium at 10x40 magnification, identifying its official drug name as Radix Liquiritiae (liquorice root). Similarly, powdered drug investigations are conducted on Iris sp. (iris or süsen) for Rhizoma Iridis and Drimia maritima (sea squill) for Bulbus Scillae using distilled water.
Organoleptic controls—which evaluate the natural sensory properties of colour, odour, flavour, and powder appearance—are combined with detailed microscopic inspections to authenticate crude plant drugs accurately and prevent adulteration in pharmaceutical preparations.
Morphological work on medicinal plant materials focuses heavily on macroscopic external features, fracture patterns, dimensions, and historical uses. Radix Liquiritiae exhibits thin cylindrical pieces with rough, brownish outer surfaces, yellowish inner surfaces, and a characteristic fibrous fracture. Smilax sp. yields Radix Sarsaparillae (saparna kökü), recognized by stripped cork layers, orange inner surfaces, and historical use by Amazonian tribes for leprosy, dermal diseases, and as a diuretic.
Uragoga ipecacuanha provides Radix Ipecacuanhae (ipeka kökü), appearing as a curled cylinder with a visible central cylinder, reddish-brown outer layers, and a fibrous fracture. Historically valued as an emetic, nauseant, expectorant, and diaphoretic, ipecac syrup was widely utilized for emergency poisoning treatments until the late 20th century.
Iris sp. rhizomes (Rhizoma Iridis) develop their characteristic violet-like odour gradually during drying from an initial earthy smell, serving primarily today as a fixative in perfumery. Orchis sp. produces Tubera Salep (salep yumrusu) consisting of mother and sister tubers; salep is exceptionally nutritious and demulcent, offering soothing relief for mucous membranes and acting as a valuable restorative diet for convalescents and children.