8 Plant Growth
Learning Objectives
- Identify common classifications of plant growth.
Water movement is the most basic classification of plant growth. All plants need water to survive and, based on how they move water, are categorized as either vascular or non-vascular. Vascular plants, such as trees, have a water conducting system, allowing them to supply aerial tissues with water and to grow well above the ground. Non-vascular plants rely on their closeness to water and their own physical absorption to support green tissues above ground. Mosses and liverworts are examples of non-vascular plants.
Reproduction is another classification of vascular plants that is based on whether they reproduce themselves asexually or sexually. Vascular plants are subdivided into two major categories, pteridophytes, and spermatophytes. Pteridophytes (Greek for “fern plant”) include ferns and horsetails that reproduce asexually by spores. Spermatophytes (Greek for “seed plant”) include conifers and flowering plants that reproduce sexually by seed.
Conifers, from the Latin for “cone-bearing” are woody plants that bear their female and male reproductive structures in separate cones or strobili rather than in flowers. Coniferous trees and shrubs typically bear both female and male cones on the same plant. Pollen produced by male cones is transported on wind currents to the female cones wherein seed development is completed. Conifers belong to the group of seed producing plants called gymnosperms. Gymnosperm literally means ‘naked seed’ as seeds are held on the surface of a cone scale or at the end of a small structure. This is the main differentiation between conifers and the flowering plants (angiosperms) which bear their seeds in an enclosed ovary of a flower that becomes the fruit.
Angiosperms are the largest and most diverse group in the plant kingdom. In addition to the presence of flowers and fruit, angiosperms are classified according to two major groups of plants that are each derived from a common ancestor species (clade), the monocotyledons and eudicotyledons. This classification is based on the number of cotyledons or seed leaves produced at seed germination. Monocotyledons (meaning “single seed-leaf”) include grasses, lilies, orchids, and palms. They develop from a seed with a single seed leaf. Some basic recognizable patterns of monocotyledons include leaf veins arranged in parallel lines; flower parts numbered in 3’s and a herbaceous plant structure. Eudicotyledons (meaning “true dicots”), are an evolutionary line that includes plants such as maples, oaks, roses, buttercups, mints, and sunflowers that develop from seed usually with a pair of seed leaves. Some basic recognizable patterns of dicotyledonous plants include leaves with netted venation; flower parts numbered in 4’s or 5’s and woody or herbaceous plant structure.
Type of growth, such as tree versus shrub or woody versus non-woody (herbaceous), is often the first visual recognition of a plant.