I have been reading the Penguin Encyclopedia of Gardening which aims to provide ‘….an explanation of words used in a technical sense in a horticultural context in the UK and USA.’ Set out as an A to Z this resulting post, missing a thousand definitions, is unlikely to rank highly with search engines.

Abscission

The separation of a leaf or fruit from it’s stem. Most notable as a deciduous tree sheds its leaves in autumn. Two layers of cells are formed to facilitate this process, an abscission layer and a corky tissue layer. The corky layer cuts off the food supply to the fruit or leaf and protects the the wound formed when the drop occurs.

Zygomorphic

A botanical term  referring to a flower having floral parts that are capable of division into essentially symmetrical halves by only one vertical or longitudinal plane passing through the axis. Examples include  Peas , Snapdragons and Orchids.

 

Orchid