Last Saturday, I was involved in giving a guided tour at the Lifestyle Corner at HortPark. The tour and showcase were aimed at educating the public what geophytes are and various common vegetables and medicinal plants that belong to this category of plants. The showcase is now on until 27 Aug 09. It will run through GardenTech 2009 (14 to 18 Aug 09 @ HortPark) and visitors to this garden fair will also get a glimpse into how one can use geophytic plant parts for home decoration!
In brief, a geophyte is a herbaceous plant with an underground storage organ. Storage organs are reservoirs of carbohydrates, nutrients and water and play an important role in the plant’s survival during adverse climatic conditions and we, humans farm them for food and medicine.
Do you know how to differentiate a taproot, tuber, rhizome, bulb or corm? These are terms that are used to describe underground vegetables such as carrots, potatoes, gingers, cocoyams and onions, respectively.
A root tuber is a modified lateral root that stores food for the plant. Either the tip, part of or the whole lateral root swells up to become a storage organ. Root tubers have the internal and external cell and tissue structures of a typical root. Unlike stem tubers, root tubers do not have nodes. Common root tubers are cassava (Manihot esculenta) and sweet potato (Ipomoea batatas).
A stem tuber is a swollen, modified underground stem that stores food for the plant. Internally, a stem tuber has the typical cell structures of a stem, including a pith, vascular zones and a cortex. Common stem tubers include the potato (Solanum tuberosum) and Chinese yam (Dioscorea opposita).
A bulb is a vertical, underground stem consisting of a compressed stem (basal plate) and modified scale-like leaves. These modified leaves serve as the primary storage tissue. Bulbs are divided into tunicate and imbricate bulbs. A tunicate bulb such as onion (Allium cepa) and garlic (A. sativum) have a paper-like covering, or tunic, that protects the scales from drying and mechanical injury. A common imbricate bulb is the edible lily bulb (Lilium sp.) which is often an additive in Chinese herbal desserts.
A corm is a vertical, underground stem that serves as a storage organ with one or more internodes. It is encased in dry, papery, dead petiole sheaths which act as a covering that protects the corm from insect attack and water loss. Corms have internal solid tissues. This distinguishes them from bulbs, which are made up mostly of layered fleshy modified leaf scales. Common corms include the cocoyam (Colocasia esculenta) and water chestnut (Eleocharis dulcis).
A taproot is a swollen, tapering root that grows vertically downwards. Lateral, fibrous roots grow out from this main taproot. Many taproots are also modified to become storage organs. Taproots can be divided into 3 main cateogries: conical root – carrot (Daucus carota), fusiform root – radish (Raphanus sativa) and napiform root – yam bean (Pacchyrhizus erosus).
A rhizome is a swollen horizontal stem of a plant. It is usually found underground, often sending out roots and leafy shoots from its nodes. A rhizome is a modified stem, and the stem tissue itself serves as the primary storage tissue. A common rhizome is the cooking ginger (Zingiber officinale).
