Most begonias can be recognized by looking at the shape of the leaves, the flowers and the size of the begonia, but if you are not familiar with the different cultivars, the American Begonia Society helps you to determine which cultivar you have or want to buy. If you are a hybridizer, you can register your begonias with the American Begonia Society. As of 2010, the begonia has approximately 1,500 different species.
Check the height of the begonia. Certain species, such as the Z-2 begonia, grow to 2 ½ feet in height and 2 feet wide; the Coco Bright scarlet begonia only grows to 8 or 9 inches in height.
Look at the leaves of the begonia. The leaves on most begonias are simple, and rarely have veins or leaflets shaped like the fingers of a hand. The leaves for different cultivars and species range from light green to dark green. Some begonia species and cultivars, such as the Coco Bright scarlet begonia, have green, red and purple leaves. The leaves might be smooth or hairy, or have smooth edges or jagged edges.
Look at the flowers on different begonias. Flowers on begonia plants are always unisexual; one plant will have only male or female flowers--never both. Flowers might be white, purple, pink or red. The sizes of the flowers are also different on different begonias. Some begonias produce flowers so small that you can barely see them, and some do not produce flowers at all.
Look at the location of the begonia, if the begonia is found growing in the wild. Some begonias prefer little sun, some prefer more sun, but a begonia will rarely be found in an area with full sun, especially in areas with long, hot summers.
Gather all the information about the begonia and take a picture of the begonia. Visit the American Begonia Society's website to compare the begonia's statistics to identify the species or cultivar.