Plants all have cellulose cell walls, higher plants form specialized tissues like aerenchyme and conductive tissues, and plant cells contain plastids.
Plants get their energy by respiration of chemical stores, generally in the form of carbohydrates, to convert adenosine diphosphate to adenosine triphosphate.
The minerals that plants need are absorbed by passive uptake as water which contains dissolved salts is drawn in from the soil by the root hairs.
Plants have limitations and needs, such as water, light and minerals, and they compete with other plants for these, both by growing upwards, and chemically.
Algae are very simple plants with common features in the ways they reproduce (always in water), and their comparative lack of specialized tissues.
The green algae are a subset of the algae, linked loosely by the chemistry of their photosynthetic pigments and their habits, the ways they grow.
Many of the lower plants such as mosses and ferns exhibit alternation of generations, with haploid and diploid forms, each giving rise to the other.
Mosses and other bryophytes make a natural grouping because they have a number of traits (lack of conductive tissue, method of reproduction) in common.
Ferns make a natural grouping, because they have similar features such as conductive tissue, and the life cycles seen in their reproductive methods.
Gymnosperms (the pines and their relatives) make a natural grouping, because they grow in similar ways, are anatomically similar, and reproduce the same way.
Higher plants have vascular tissue systems with phloem and xylem, which allows them to rise up off the ground, and get more energy from the Sun.
Higher plants have complex leaf tissue systems, with an epidermis with stomates, and an inner area, rich in chloroplasts and air gaps to allow air access.
Higher plants have root tissue systems which are able to gather in the water and minerals that the plant needs. Some roots have symbionts attached.
Higher plants have growth areas within them: cambium and meristem in particular, where new cells are formed and differentiated into the needed tissues.
Wood is a two-phase material, with lignin for rigidity and cellulose fibres for tensile strength, which plants need to get higher than other plants.
Some plants are annual, growing through a complete cycle once a year (or more often in some cases), some are perennial, lasting for many years, like trees.
Flowering plants or angiosperms may be divided into dicotyledons and monocotyledons, which have other traits such as the forms of leaves and roots in common.
Angiosperms have different ways of getting pollen to travel from one plant to another, relying on wind, birds, insects, and even small mammals in some cases.
Angiosperms have a variety of ways to spread their seeds to new areas, using wind, the digestive systems of animals, hooks and adhesives among other things.
Angiosperms often hybridize outside their species though usually within their genus, but sometimes further afield, if tetraploid individuals occur.
Higher plants have a range of tissue systems, with different types of cell in different parts, performing different functions to maintain the plant.
At times of stress, the leaves of angiosperms drop off at the abscission layer, a point where the plant seals itself off to prevent undue water loss.
Dying leaves are yellow because, before a leaf is dropped from a plant, most of the available nutrients are taken back into the plant, to be used again.
Many angiosperms produce alkaloid poisons in their leaves to defend them against herbivores, and the herbivores need to evolve ways to deal with this.
Angiosperms can also exchange genetic material outside species barriers when microbes carry genes into plants, a process called horizontal gene transfer.
Angiosperms sometimes produce adventitious roots from branches, providing new sources of water and support for large trees, once the roots are established.
Roots are used by plants to obtain water and minerals, generally from the soil, but roots also keep plants upright against the forces of gravity and wind.
Plants can sense the down direction, and roots grow downwards, although once in the soil, the secondary roots of many plants will also grow towards water.
Pollen fertilizes a flowering plant when a pollen tube grows down the style, so one of the nuclei can travel down the tube and fuse with a nucleus in the ovum.
In the laboratory, plant hybrids can be created that cross species barriers, but the same process also happens in nature, and in agriculture.
Many plants have spines or hairs on their leaves and stems to discourage herbivores from grazing on them, depriving the plant of water, energy and minerals.
Over time, plants have evolved to produce chemicals that attract useful animals such as pollinators, while also making chemicals that repel potential predators.