From DT Online
The Taxonomy of the plant Kingdom classifies trees as either Angiosperm (encased seeds) or Gymnosperm (naked seeds). These sub-divisions are each sub-divided into Genus (a subgroup of organisms that have many common characteristics such as oaks or pines) then Species which can be thought of as a specific kind of tree - but this too can be further sub-divided into Varieties for example.
Examples growing in the UK include: Pines, Firs, Larch, and Spruce. Yew is also a Softwood even though it is quite hard - the distinction between Hardwood and Softwood is not determined by how hard or soft they are.