According to the nature of the stem the plants are often classified into groups:- 1. Herbs 2. Shrubs 3. Trees 4. Trailers 5. Climbers.
Group # 1. Herbs:
These are the small plants with soft stems having scanty woody tissues. On the basis of duration of life, herbs may be annuals, biennials and perennials. If they grow for only one season and complete life cycle during that period, they are called annuals, e.g. mustard, Balsam (B. Dopati), paddy, jute.
Those which complete their life cycle in two seasons are called biennials. In the first season the biennials manufacture and store sufficient food and in the next season they bear reproductive organs, e.g. English radish, carrot.
It is to be noted that these plants are biennials in cold countries but in our country they grow as annuals. If the plants continue for more than two seasons, they are called perennials. Banana, ginger, Carina (B. Sarbajaya), are perennial herbs.
Group # 2. Shrubs:
These are woody plants which produce so many branches that the main stem often cannot be distinguished. Shrubs are perennial plants, e.g. Hibiscus (B. Java), pomegranate, Duranta (B. Mehdi).
Group # 3. Trees:
These are tall woody plants with distinct pillar like main axis or trunk, e.g. mango, banyan, palms. Trees which shed their leaves at a particular season of the year are called deciduous; whereas those which have no definite period for shedding leaves are called evergreen.
Group # 4. Trailers:
These are the weak-stemmed plants which just trail horizontally on the surface of the soil. Some of them do not bear roots at the nodes and are called procumbent, e.g. Basella (B. Puin); but sweet potato, Cynodon (B. Durboghass) and many other grasses bear roots at the nodes to fix themselves to the soil. They are called creepers.
Group # 5. Climbers:
These are the weak plants which grow upright only with the help of some kind of support.
They are classified into following types according to their modes of climbing:
(a) Root Climbers:
Betel, vine, Scindapsus (B. Gaj-pipul), etc., climb with the help of adventitious roots from the stems which, in fact, cling to the support on which the plant climbs (Fig. 42).
(b) Hook Climbers and Scramblers:
Many weak plants produce hard, pointed hook-like bodies for climbing. Artabotrys (B. Kan-thali champa) bears hooks on the floral axis (Fig. 52, 3). Pointed prickles are present in many wild roses and canes for the same purpose.
(c) Tendril Climbers:
Tendrils are the slender leafless bodies remarkably sensitive to contact. As soon as they come in contact with any support they quickly coil round it and thus help the plant in climbing. Plant-parts like stems (Fig. 52, 1), leaves and even floral axis are modified into tendrils. Examples—Cucurbita (B. Gourd), pea, Smilax (B. Kumarika), Antigonon.
(d) Leaf Climbers:
Parts of the leaves of some plants also coil round the support. The leaf stalks of Clematis (Fig. 52, 2) and Nepenthes (Pitcher plant, Fig. 177, 1), leaf tip of Gloriosa (B. Ulat chandal, Fig. 68, 6), are good examples.
(e) Stem climbers or Twiners:
Some plants twine round the support by their weak slender stems and branches, having no specialised structures for the purpose. They may twine clockwise as in Dolichos lablab (B. Sheem), or may twine anti-clockwise as in Clitoria (B. Aparajita) and Ipomoea quamoclit (B. Tarulata, Fig. 53).
(f) Liane or Woody Climbers:
These are fast growing woody plants which twine round the stems and branches of tall trees and thus go up in search of light and air. Examples—Quisqualis (Rangoon creeper), Hiptage madhablata (B. Madhabilata).