Plant Structure

Web Lecture

• Plant Classification by Structure
• Roots, Stems, and Leaves
• Plant Tissues

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The Parts Common to (almost) all Plants

The study of plants, or botany looks at all aspects of plant life, from plant anatomy (parts and structures) and physiology (plant functions) to plant growth, reproduction, and function within a habitat. For the next few sessions, we will focus on general characteristics shared by large groups of plants, focussing specifically on angiosperms, which are the source of most of our plant food.

Plant Classification by Structure

We classified plants earlier in our survey of living things into four main groups, according to their overall reproductive mechanisms: mosses, ferns, gymnosperms, and angiosperms. Angiosperms are further dived into monocot and dicot groups.

Class	Example
Bryophytes These are non-vascular plants including mosses and liverworts. Notice the sporangia (extended brown shoots) and the dominant gametophyte (green mass) of the moss. The light-colored growth is lichen, a symbiotic relationship between mosses and fungi.
Ferns These vascular plants do not produce seeds, but instead reproduce using spores. Below is a typical temperate rain forest fern.	Ferns develop spores on their sporangia (dominant structure). Here is the reverse side of a sword fern frond, showing spores.
Gymnosperms As vascular plants with "naked" seeds, the seeds of gymnosperms are not enclosed in a protective coating. Below are the developing young cones of a Douglas Fir. Each scale is a seed, which will eventually separate from the cone, ready to receive pollen for fertilization.
Angiosperms This class includes all plants with vascular plants with flowers. The wild rose below has five petals and netted veins in its leaves, making it a dicot. Its colorful petals attract insects and birds, which pick up pollen from the anthers (yellow stalks) and distribute them to other flowers.
Monocots: plants with one leaf during first growth, leaves with parallel veins, flowers with parts (petals, anthers) in groups of three, fibrous root systems, and complex vascular bundals.	Dicots: plants with two leaves during first growth, leaves with netted veins, flowers with parts in groups of four or five, a taproot, and vascular bundles arranged in a ring.

Classifying Monocots and Dicots

Considerations	Challenges
Contrast the long, thin, straight blades with parallel veins (monocts), with the round or pear-shaped leaves with netted veins (dicots).	Fused and bell-shaped flowers may be difficult to classify as monocots or dicots by flower Examining the petals, however, shows this plant is a dicot from the 5-petal arrangment hosting the flowers.

Roots, Stems, and Leaves

All plants, regardless of their classification, have some form of roots, stems, and leaves as part of the individual organism's structure. The pictures above show a variety of plant leaves, including the small water-retaining stubby leaves of mosses, the needles of the Douglas Fir, the fronds of ferns, and the netted leaves of the wild rose. The primary purpose of the leaf is to collect sunlight to support photosynthesis, but leaves may also take on thorny shapes to protect the plant, or sticky suckers to help the plant climb toward sunlight.

The tips of stems are where "first" or primary growth appears. In spring, new growth appears as lateral as well as apical buds. In the picture to the right, a single structure at the apex of the stem will form a cluster of new flowers.

Plants may also store food in stems. Tubers (potatos), bulbs (tulips), corms (gladiolas), and other underground stem structures allow plants to pack away starches and water as resources when food availability is low or during dry seasons, including cold climates where snow replaces rainfall for part of the year.

Plant Tissues

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