Lobelia refers to a genus of flowering plants that encompasses over 400 different species, including annuals, perennials, and even shrubs. This wide botanical family is popular in gardens due to its long flowering period and the intense color of its blooms. The striking flowers and ease of growth have made many types a common sight in both ornamental plantings and natural landscapes.
Distinguishing the Major Types
The appearance of a Lobelia plant depends heavily on the specific species, which generally fall into two broad structural categories: low-growing annuals and tall, upright perennials. The most familiar type is the Edging or Trailing Lobelia (Lobelia erinus), a tender perennial usually grown as an annual. This variety forms dense, low-growing mounds or spreading mats, typically reaching four to nine inches in height with a cascading habit well-suited for containers and hanging baskets.
In contrast, perennial types like Cardinal Flower (Lobelia cardinalis) and Great Blue Lobelia (Lobelia siphilitica) exhibit a completely different structure. These species are robust, upright herbs that develop from a basal rosette of leaves and send up sturdy, often unbranched, flower stalks. Mature perennial plants often reach impressive heights of two to four feet. This difference in overall stature and growth habit is the clearest visual distinction.
Flower Structure and Color Palette
Despite the diversity in overall plant size, the flowers across the Lobelia genus share a distinct and recognizable structure. The blooms are uniformly tubular and two-lipped, typically divided into five separate lobes. Two of these lobes are often smaller and erect, while the remaining three fan out to form a larger lower lip. This irregular shape distinguishes them from the simple bell-shaped blossoms of many other plants.
The flowers of the low-growing annual L. erinus are small, usually measuring about half an inch long, and are borne prolifically in loose clusters along the trailing stems. These flowers are famous for their intense blue and purple shades, but they are also available in pink, white, and reddish-purple. Often, these tiny blooms feature a contrasting white or yellow throat.
For the tall, upright perennials, the flowers are arranged densely on tall, terminal spikes or racemes. Lobelia cardinalis is defined by its striking, intense scarlet-red flowers, which are larger and more tubular than the annual types. In contrast, Lobelia siphilitica typically displays bright blue to purplish-blue flowers along its spikes, although white forms also exist. These perennial varieties often produce hybrids, such as Lobelia × speciosa, which offer a wider palette, including pink, lavender, and various shades of red and purple.
Foliage and Stem Appearance
The foliage of the Lobelia species is generally simple and arranged alternately along the stems. The leaves are commonly lance-shaped or oval, with size and texture varying significantly based on the species. For the annual trailing L. erinus, the leaves are small, narrow, and linear, often appearing light green. The stems of this type are delicate, herbaceous, and highly branched, which contributes to the plant’s dense, mounding appearance.
The upright perennial varieties feature more substantial foliage. L. cardinalis and its related hybrids often have leaves that range from bright green to a deep bronze or purple-tinged hue. These leaves form a basal rosette at the base of the plant, from which the thicker, rigid flowering stems emerge. The stems themselves can be green or sometimes tinged with red, providing sturdy support for the heavy flower spikes.