plant identification for beginners

When I decided to name, list and photograph the plants in the garden I had no idea that plant identification was an ambiguous slippery minefield. 
Wikipedia has a neat definition of plant identification: Plant identification is the determination of the identity of an unknown plant by comparison with previously collected specimens or with the aid of books or identification manuals. The process of identification connects the specimen with a published name. Once a plant specimen has been identified, its name and properties are known.

Plant classification gets very complicated. It seems the main elements  relevant to gardeners, as opposed to botanists, are Family, Genus and species. The categories of subspecies, Varieties and Cultivars are also useful in identifying a particular plant.

Here are some definitions and glimmers of understanding that I have picked up along the learning journey.

Plant families: Plants are grouped into families based on similarities in their structures.  Knowing about plant families makes the bewildering amount of information more manageable. For example, all members of the family of Campanulaceae have blue star or bell shaped leaves.  

Genus: This is the name we give plants belonging to a particular group, e.g Papaver (Poppies)

Species: This is the level that defines an individual plant. Often, the name will describe some aspect of the plant - the colour of the flowers, size or shape of the leaves, or it may be named after the place where it was found. Together, the Genus and species name refer to only one plant, and they are used to identify that particular plant.

Cultivars: a combination of the words cultivated and varieties. According to the Australian Cultivar Registration Authority,  cultivated plants are "plants raised in cultivation which differ sufficiently from their wild ancestors or, if taken into cultivation from the wild, are worthy enough of distinction from wild populations for horticultural purposes to merit special names.”

Cultivars are maintained by the use of cuttings to produce stable, repeatable forms. (Propagation using seeds leads to unpredictable outcomes).

Types of cultivars:

Hybrids: A hybrid is the result of crossing two plant species, either deliberately or accidentally.

Natural mutations: These can occur within a wild or garden setting.   A plant’s genetic component can change markedly, so, for example, it may produce a totally new colour or it may revert to an earlier colour.  

Varieties: Varieties are plants that have differences from the species plant.

Forms: A form is a plant within a species that has minor botanical differences, such as the colour of flower or shape of the leaves. 

Modern cultivars often lack the delicacy, charm and variety of old fashioned plants - think roses.  In relation to vegetables, a preference for hybrids  bred for uniformity and longer shelf life, has contributed to the decline in heritage vegetables and biodiversity. 

You can't afford to get too comfortable in this field of knowledge.  The plants themselves are continually evolving into new varieties and forms, just asking to be identified and understood.  Plant names and family membership also change as plant bosses find better ways of organizing plant knowledge.  

For example, take Eriostemon, a genus of flowering plants belonging to the family Rutaceae. A large number of species once classified within the genus were then moved into the newer genus Philotheca. I used to grow Eriostemon in the garden, appreciating its starry white flowers and its resilience.  Now I no longer grow Eriostemon. Now I grow Philotheca, although they look and grow exactly the same.