The word “lily” is frequently used in common language to describe many beautiful flowers that are not botanically related, which leads to confusion about the actual types available. To understand how many distinct varieties exist, one must first focus solely on the plants belonging to the Lilium genus. This genus represents the group of plants known as “true lilies,” all of which share specific genetic and structural characteristics. The vast array of hybrids and cultivars that gardeners encounter are all descendants of a relatively small number of original species.
Defining the True Lily
True lilies are herbaceous perennials that originate from a unique type of underground storage organ called a scaly bulb. Unlike the bulbs of a tulip or daffodil, a true lily bulb lacks a protective outer tunic, instead consisting of numerous overlapping, fleshy scales. When the plant flowers, it produces large, prominent blossoms with six tepals—a botanical term for petals and sepals that look identical—often displaying six prominent stamens.
Many popular garden flowers carry the “lily” name but belong to completely different plant families, making them “false lilies.” For instance, the Daylily (Hemerocallis) grows from tuberous roots, not a scaly bulb. The Calla Lily (Zantedeschia) and the Peace Lily (Spathiphyllum) are members of the Araceae family, while the Water Lily (Nymphaea) belongs to a separate order of plants. Distinguishing these groups is based on their fundamental botanical structure.
The Nine Horticultural Divisions
While there are approximately 100 to 117 naturally occurring Lilium species, the “types” most often referenced by gardeners are categorized into nine Horticultural Divisions. This classification system was established by the Royal Horticultural Society to organize the thousands of complex hybrids based on their parent species and shared characteristics. The first eight divisions are reserved for hybrids, while the ninth division is for the original, unaltered species.
The nine divisions categorize lilies based on their parentage and shared traits:
- Division I: Asiatic Hybrids are the most widely grown due to their hardiness and ease of cultivation. They feature vibrant, upward-facing flowers that are typically unscented.
- Division II: Martagon Hybrids are characterized by small, numerous, downward-facing flowers with strongly recurved tepals, often called “Turk’s Cap” lilies.
- Division III: Candidum Hybrids are a smaller group based on the classic European species, Lilium candidum.
- Division IV: American Hybrids are derived from North American species, often featuring Turk’s Cap flowers and preferring slightly acidic, woodland conditions.
- Division V: Longiflorum Hybrids are best known for the Easter Lily, which has large, pure white, trumpet-shaped flowers.
- Division VI: Trumpet and Aurelian Hybrids are tall, robust lilies with large, funnel-shaped flowers and a strong, sweet fragrance.
- Division VII: Oriental Hybrids are popular for their huge, often heavily spotted flowers and powerful, spicy scent, typically blooming later in the season.
- Division VIII: Interdivisional Hybrids are complex crosses made between the other seven hybrid groups, such as Orienpet (Oriental x Trumpet) or LA (Longiflorum x Asiatic) hybrids.
- Division IX: This division includes all the Lilium species themselves, which are the wild, naturally occurring lilies from which all the others were bred.
Selecting Lilies Based on Division
The horticultural divisions act as a practical guide for selecting the best lily for a specific garden situation. Asiatic Hybrids are the ideal choice for gardeners seeking an early burst of color, as they bloom in early to mid-summer. They are compact, generally growing between two and three feet tall, and their lack of fragrance makes them excellent cut flowers.
Oriental Hybrids bloom later, from mid-to-late summer, producing massive, intensely fragrant flowers that can perfume an entire garden area. These varieties generally demand richer, more acidic soil conditions compared to the adaptable Asiatics. Trumpet and Aurelian Hybrids offer an alternative fragrant option, known for their height, often reaching six feet, and their classic, elongated trumpet shape.
For those looking for the vigor and stature of a “tree lily,” the Interdivisional Hybrids, particularly the Orienpets, are the best selection. These types combine the fragrance and bloom size of Orientals with the hardiness and height of the Trumpets. They result in plants that can tower over seven feet.