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The Cacti and Succulents - Introduction

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Cacti (plural of cactus) and succulents are xerophytic plants. Xerophytes derived from two Greek words ‘xero’ means dry and ‘phytus’ means plant, hence these are the plants which are adapted to dry habitats and crassulacean acid metabolism (fixation of carbon dioxide in plants in arid or semi-arid conditions) is their characteristic phenomenon (Ingronille and Eddie, 2006). Xerophytes belong to deserts of special geographical conditions with specific climate and its flora and fauna. The xerophytes developed over very long period in Eocene era. The meaning of xerophytes derived from a Greek words ‘xero’ means dry and ‘phytus’ means plants, which means the dry plants. Characteristically the xerophytes are the plants which are well adapted to shortage of water by retaining the water in various parts of body viz. leaves, stems and roots for a very long period.


Cactus word has been derived from Greek word ‘Kaktos’ which means thistle (Frank, 1974). Typically a cactus possesses a perennial photosynthetic succulent stem, bearing leaf spines produced on modified axillary buds, termed as areoles, but lacking broad green leaves (Nobel, 2002).

The succulent word has been derived from Latin word Succulentus (Chidamian, 1984), which mean juicy and fleshy. A succulent is plant possessing at least one succulent tissue (Sajeva and Castanzo, 1997). “A succulent is a living tissue that, besides possible other tasks, serves and guarantees at least temporary storage of utilizable water, which makes the plant temporarily independent of an external water supply when soil water conditions have so deteriorated that the root is no longer able to provide the necessary water from soil”. They are all draught-resistant plants especially adapted to taking up and restoring great quantities of water in different parts of the plant viz. leaves, stems and roots.

All succulents are not cacti but all cacti are succulents. The Cacti are typical succulent perennials. Cacti have areoles which are absent in other succulents. Areole is a cluster of axillary buds. Shoots, spines and flowers emerge from areoles. The areoles have various shapes and arrangements e.g. in some they are masses of spines that all more or less equal in shape and size; some have longer, more massive spines in the center and shorter, thinner spines around the edges; others have hooked or straight spines (James et. al., 2002). The succulents have reduced number of areoles which not reduces water losses but the amount of carbon dioxide intake.

In CAM the stamata of plants open at night, when temperature is lower and the humidity of the air is higher. These plants store carbon dioxide, using organic acid – namely malic acid – during the night when stomata are open. Carbon dioxide is released during the day when stamata are closed but light is available for photosynthesis to transport the carbon dioxide into sugars. CAM is not only efficient the economic use of water but is also highly effective in capturing carbon dioxide from air.

The Halophytes and epiphytes are also xerophytic plants. The halophytes grow in salty lands and the epiphytes grow over other plants and take nutrition from host plant.

  

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