Lilies (Lilium)

The plants of the genus Lilium are the true lily plants, comprising a genus of about 100 species in the family Liliaceae. Lilies are usually erect leafy stemmed herbs. The majority of species form naked or tunic-less scaly underground bulbs. In some North American species the base of the bulb develops into rhizomes, on which numerous small bulbs are found. Some lilies develop stolons.

Many species form stem-roots. With these, the bulb grows naturally at some depth in the soil, and each year the new stem puts out adventitious roots above the bulb as it emerges from the soil. These roots are in addition to the basal roots that develop at the base of the bulb. The large lily flowers have three petals along with three petal-like sepals, often fragrant, and come in a range of colours ranging through whites, yellows, oranges, pinks, reds, purples, bronze and even nearly black. Markings include spots, brush strokes and picotees.
The plants are summer flowering. Most lilies are deciduous, but Lilium candidum bears a basal rosette of leaves for much of the year. Flowers are formed at the top of a single erect stem, with leaves being borne at intervals up the stem.

Classification of garden forms

Numerous forms are grown for the garden, and most of these are hybrids. They vary according to their parent species, and are classified in the following broad groups:

Species (Division IX). All natural species and naturally occurring forms are included in this group. Species lilies require specialized care due to their different natural growing conditions through-out the world. Anyone endeavouring to grow these varieties needs to research their growing requirements. Species bulbs for the most part are smaller than hybrid varieties, but will produce good quality stems and blooms. Their delicate, beautiful flowers will be well worth the effort required.
Asiatic hybrids (Division I). These are lilies with medium sized, upright or outward facing flowers, mostly unscented. They are derived from central and east Asian species. Asiatic (or Asian) hybrids, are characterized by open, often upward-facing flowers, most often with bright colors (orange, yellow, red, pink, white); they are not known for scent. These hybrids have from four to eight calyxes (buds) per stem.
Martagon hybrids (Division II). These are based on L. martagon and L. hansonii. The flowers are nodding, Turk's cap style (with the petals strongly recurved). These dainty flowered ones are fast becoming popular, with as many a 50 flowers on tall erect stems with whorled leaves. These lilies often take a year to settle in and are known to sulk the first growing season, sometimes not showing any presence until the next growing season. Once established in the border or garden they can be left alone for many years. They are the only lilies that prefer dappled shade.
Candidum hybrids (Division III). This includes hybrids of L. candidum with several other mostly European species.
American hybrids (Division IV). These are mostly taller growing forms, originally derived from L. pardalinum. Many are clump-forming perennials with rhizomatous rootstocks.
Longiflorum hybrids (Division V). These are cultivated forms of L. longiflorum and its subspecies. They are most important as plants for cut flowers, and are less often grown in the garden than other hybrids. Longiflorum hybrids are characterized by large trumpet-shaped flowers which stand horizontally on the stems (e.g. Easter lilies and Christmas lilies). In the United States, Longiflorum lilies are most often seen as potted plants, although in Europe and Australia, they're widely enjoyed as cut flowers.
Trumpet lilies (Division VI), including Aurelian hybrids. 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 (Division VII). These are based on hybrids of L. auratum and L. speciosum, together with crossbreeds from several mainland Asiatic species. They are fragrant, and the flowers. Plants tend to be tall, and the flowers may be quite large and tend to be outward facing. The blooms of Oriental hybrids are usually much larger and more flamboyant than those of Asiatic hybrids, and most are heavily scented. Oriental lilies generally are more expensive than Asiatic lilies; their cultivation is more difficult and takes longer than that of Asiatics, and the bulbs are more expensive. They average four or more calyxes per stem. An example is Lilium "Stargazer".
Other hybrids (Division VIII). Includes all other garden hybrids.