Classification of Lilies
Many forms of lilies are grown for the garden, containers, and florists and most of these are hybrids. They vary according to their parent species, and are classified in the following broad groups;
Asiatic hybrids. These are plants with medium sized, upright or outward facing flowers, mostly unscented. They are derived from central and East Asian species.
Martagon hybrids. These are based on L. martagon and L. hansonii. The flowers are nodding, Turk’s cap style (with the petals strongly recurved).
Candidum hybrids. This includes hybrids of L. candidum with several other mostly European species.
American hybrids. These are mostly taller growing forms, originally derived from L. pardalinum. Many are clump-forming perennials with rhizomatous rootstocks.
Longiflorum hybrids. These are cultivated forms of this species and its subspecies. They are most important as plants for cut flowers, and are less often grown in the garden than other hybrids.
Trumpet lilies, including Aurelian hybrids (with L.henryi). This group includes hybrids of many Asiatic species, including L. regale and L. aurelianse. The flowers are trumpet shaped, facing outward or somewhat downward, and tend to be strongly fragrant, often especially night-fragrant.
Oriental hybrids. These are based on hybrids of L. auratum and L. speciosum, together with crossbreeds from several Japan native species. They are fragrant, and the flowers tend to be outward facing. Plants tend to be tall, and the flowers may be quite large. An example is Lilium “Stargazer”.
Other hybrids. Includes all other garden hybrids.
Species. All natural species and naturally occurring forms are included in this group.
Many newer commercial varieties are developed by using new technologies such as in vitro pollination, ovary culture and embryo rescue.
The best growing zones for all classes are:
Divisions I and II: USDA Zones 3 – 8
Divisions III – IX: USDA Zones 4 – 8
All Classes can be grown in zones 9 & 10 if dug up every year and refrigerated before planting.
Reference: Wikipedia Encyclopedia