Sub-family Lobelioideae has around 30 genera and 1200 species.
Lobelia is the largest genus with 415 species and 7 of the 39 Australian natives are seen in S. E. Queensland.
There are 2 naturalized species and more natives are still being described.
It is a very variable genus with plants of vastly different habits, shapes, sizes, flower structure and colours and fruit.
Characteristics of typical plants include resupinate (upside down) bilaterally symmetric flowers with fused anthers.
They are mostly annual or perennial herbs with a few shrubs and some trees up to 9 m high.
Many of the herbs are low mounding or trailing plants with prostrate to erect stems.
Hairs may be present on leaves, pedicels and flowers and they have a milky latex.
Alternately arranged leaves can be in a basal rosette with or without an erect stem with sparse to dense leaves.
Leaves may have a petiole (stalk) or the base of the blade may taper to an indistinct or no petiole.
They can be a few mms up to 40 cm long with blades of almost any shape from linear to wide or narrowly
ovate, elliptic or obovate to almost round and lance or spoon-shaped.
The base can be rounded, flattish or heart-shaped and the edges smooth, lobed or toothed.
Inflorescences may be a number of solitary axillary flowers along the upper part of the stem.
When there is a gradual change from small upper stem leaves to similar leaf-like bracts inflorescences appear to be a terminal spike (raceme or cyme).
These may have a peduncle with bracts at the base and some are branched (a panicle).
Flowers may be on a stalk (pedicel) a few mms up to 7 (10) cm long sometimes with a pair of opposite leaf-like bracteoles at the base.
Bracteoles can be as small as 0.1 mm and bracts up to 7 or 8 cm long.
Descriptions of the perianth are after the pedicel twists the flower upside down (resupination).
The sepal and petal bases are fused into a hypanthium a few mms long.
The 5 erect or spreading sepal lobes on the hypanthium may have small teeth.
The corolla tube, on the hypanthium has 5 lobes that may be around the same size forming a rotate radially symmetric corolla.
Typically the tube has 2 lips (bi-labiate) and is split almost to the base on the upper side.
The upper lip has 2 narrow erect lobes and the lower lip 3 larger spreading lobes.
There are often 2 pouch-like swellings into the throat of the lower lip (gibbous).
Some species have a long or short slender nectar spur at the base of the corolla tube.
Blue and purple are the main colours but many flowers have 1 or 2 more including areas of yellow, white, red, pink or orange
mainly in the throat which may have some small hairs.
Flowers are mostly bisexual but some are unisexual with males and females on different plants.
These differ by males having a small ovary and females sterile anthers.
The 5 stamens are inserted onto the base of the corolla tube or the top of the hypanthium.
The filaments are free to mostly fused and the anthers are fused into an anther tube.
Anthers may be of different lengths and with no hairs or a few to many short ones on the tip of some or all.
Basifixed anthers open inwards.
The inferior or mostly inferior ovary has 2 locules with numerous ovules and 1 style with a bi-lobed stigma.
There are usually hairs on the upper part of the style to collect pollen as it grows through the anther tube.
Fruit are almost always variously shaped loculicidal capsules that open into the chambers through apical valves.
The sometimes 3-angled seeds may have a smooth or patterned surface.
Species plants seen in Australian nurseries include Lobelia aberdarica, L. anceps,
L. cardinalis, L. erinus, L. gibbosa, L. inflata, L. membranacea and L. siphilitica.
Most plants are hybrids and cultivars and they come in mounding, trailing and tall to dwarf forms
with blue, purple, pink, red, lavender and white flowers some with a white eye.