Introduction

Organisms on Earth were traditionally sorted into just two groups, plants and animals, based mainly on how they get their nutrition, whether they can move about, and whether their cells carry a wall - and under that older scheme, Bacteria, Fungi, Algae, Bryophytes, Pteridophytes, Gymnosperms and Angiosperms were all lumped together as 'plants'. Molecular-level evidence has since shown Bacteria and Fungi to be fundamentally distinct lineages, and both have since been moved out into their own separate kingdoms. Botany itself is among the oldest of the sciences, its roots reaching back to when early humans first began exploring and identifying plants to meet basic needs - food, clothing, medicine, shelter. What makes plants genuinely unique among living things is their capacity to capture the sun's light energy and convert it into stored chemical energy as food, through the remarkable process of photosynthesis - a process that not only feeds nearly every other living thing but also draws down carbon dioxide from the atmosphere, easing one of the major greenhouse gases driving global warming. Plants themselves range enormously in scale, from microscopic algae to towering, highly evolved angiosperms, and the plant world is full of its own mysteries - in size, shape, habit, habitat and modes of reproduction - even though every plant, at bottom, is built from the same basic unit: the cell.