There are about 55 different species in the genus Malus, and there are innumerable cultivars available in the landscape trade. The Morton Arboretum's Crabapple Collection was started in 1924. Part of this collection on the West Side participated in the National Crabapple Evaluation Program which evaluated new and disease-resistant varieties. As a result of the multi-year evaluation and additions, it has transformed into the West Side Malus Collection which now contains 60 different kinds and over 140 specimens with highly desirable qualities.
Some of the specimens in this collection are almost large enough to be considered shade trees, while others are quite small. There is a great variety of shape as well, from wide to upright and narrow, weeping, and multi-stemmed. There is variety in flower color, ranging from white to pink, red, purple, and crimson. Some flower buds will be one color, and then open up to a completely different color! Fruits range in size from smaller than a pea, to nearly the size of most apples; they can be red, purple, orange, yellow, or green. Some of the smaller fruits persist on the tree throughout winter, providing a splash of color in the cold months.