Wood Types
Plants with true wood (wood produced from a vascular cambium) have different forms during geologic history
Origin of Wood
Secondary xylem (wood) has evolved several times during geologic history. The following details the independent origins of secondary xylem that are known from the fossil record:
Cormose lycophytes (e.g. Lepidodendrales) evolved wood in the Late Devonian
Early euphyllophytes (e.g. Armoricaphyton) from the Early Devonian is the earliest known woody plant in the fossil record
This plant may have given rise to woody growth in the horsetails and lignophytes
Arborescent horsetails (e.g. Calamitaceae) in the Mississippian
Lignophytes (e.g. Progymnosperms, Spermatophytes) in the Late Devonian
Manoxylic wood
Secondary vascular tissues with large amounts of softer storage cells (i.e. parenchyma) mixed with the wood or xylem cells (e.g. tracheids).
The stems of these plants are softer than the wood of trees we use for lumber.
Examples of plants with manoxylic wood are cycads, the spurs or short shoots of Ginkgo trees, as well as many extinct seed fern groups including Callistophytes†, Lyginopterids†, Medullosids†, Calamopityales†, and Buteoxylonales†
Pycnoxylic wood
Secondary vascular tissues with copious amounts of xylem cells (e.g. tracheids) and little parenchyma.
This wood is much stronger and durable.
Examples of plants with pycnoxylic wood are conifers or cone-bearing trees, the long shoots of Ginkgo, and angiosperms
Hardwoods versus softwoods
The above terms should not be confused with the terms "hard" versus "soft" woods. These terms are used by agro-foresters to make a distinction between conifer trees (soft wood) and angiosperm trees (hard wood)
Conifers (mostly evergreen cone-bearing trees such as pines) have wood that is light-weight, light in color, and strong in tension, but weak in shear (along the grains). Therefore this is called "soft wood", which is usually cheaper and used for building inexpensive furniture or used for paper pulp.
Flowering plants (mostly deciduous trees such as oak/maple) have wood that is darker in color, heavier in weight, and strong in compression, tension, and shear. Therefore this is called "hard wood", which is used to make durable furniture, flooring, and building structures