Utricularia geoffrayi and Utricularia minutissima have been frequently confused with each other, with many misidentified plants in cultivation and in scientific collections. Formal descriptions of the taxa fail to fully describe the wide variation in morphological characteristics, both due to immediate environmental influences and stable differences across their broad range from Australia, through South East Asia and Indochina, to East Asia. I have observed both species in Australia and will discuss characteristics and taxonomy to hopefully clarify their identity. Note that these descriptions refer specifically to the Australian plants as I have not observed them overseas.
In Australia, there are two main groupings of plants, each with stable characteristics that are easily distinguishable in the field. The following descriptions are formed from my observations of the plants in nature across Queensland and the Northern Territory, Australia. They might not necessarily match overseas specimens.
The first of these groups – Utricularia geoffrayi (Figure 1) – is the larger of the two taxa. U. geoffrayi typically has purple blooms around 1 cm in length. In fully developed blooms, the lower corolla lip is domed in the middle, usually with two humps near the palate, and has three variably shallow lobes at the extremity. The upper corolla lip is shorter than the lower corolla lip, and curves forward noticeably. The spur is about twice as long as the lower corolla lip and terminates with a point that is sometimes it is slightly divided at the apex. It is almost always thrust forwards such that it is positioned more or less horizontally. The flowers are usually purple and white in colour, with two characteristic yellow dots near the palate. The flower stalk typically reaches around 5 cm tall and normally has two to four blooms, with one active flower forming at a time.
The second group – Utricularia minutissima (Figure 2) – encompasses smaller plants that are various intensities of pink. These blooms are about half a centimetre in length. In fully developed blooms, the lower corolla lip has a single broad dome towards the palate, and three variably deep lobes at the extremity. The upper corolla lip is small and upright and slightly tilted forward. The spur is longer than the lower corolla lip, and terminates in a blunted/truncated two-pointed apex. Usually, the spur is moderately thrust forwards such that it usually points downwards at an angle. The flowers are coloured in various intensities of pink, and often white towards the palate. The flower stalk is usually around 2-4 cm long with one or two blooms, with one active flower occurring at a time.
Both species have considerable variation due to immediate environmental conditions. U. minutissima often forms semi-developed and cleistogamous flowers which don’t fully open if at all (Figure 2 a). In the tropics, it is common to find a tiny closely-related taxon with flowers about 1 mm in length (Figure 2 b). Since the size of the plants inhibits floral development, it is unclear whether they represent a new taxon or just an unusual growth phase of the species. In U. geoffrayi, stunted flowers are very common, especially in drying conditions (Figure 2 c). In these stunted flowers, the lobes of the lower corolla lip are often misformed and the spur can be strongly curved upwards.
Both Utricularia geoffrayi and U. minutissima are common across northern Australia, in regions influenced by the monsoon that have distinct wet and dry seasons (although U. minutissima extends to SE Queensland). U. geoffrayi is more commonly associated with tropical savannah and grows in seasonal seepages and soaks near creeks, usually in wet brown sand and clay amongst grasses (Figure 3 a). U. minutissima is more frequently observed in coastal heathland and prefers silica sand (Figure 3 b). Nonetheless, both taxa are often found growing side-by-side in habitats where both their niches are present.
The following table summarises characters that can easily be used to distinguish Utricularia geoffrayi and U. minutissima in Australia. Given the variation in the taxa across its geographic range, it may be inaccurate for specimens overseas.
|Character||Utricularia geoffrayi (Figure 4 a)||Utricularia minutissima (Figure 4 b)|
|Colour of bloom||Mostly purple. White towards the palate. Two yellow ‘eye dots’ near the palate.||Various intensities of pink. Often white towards the palate.|
|Spur||Apex is comparatively sharp. Distal end of spur is orientated more or less horizontally (often bends upwards in stunted blooms).||Apex is comparatively blunt. Distal end of spur usually points forward and downward at an angle.|
|Size||Larger. Blooms typically around 0.8-1 cm in length. Height of flower stalks often exceeding 4 cm.||Smaller. Blooms typically around 0.4-0.6 cm in length. Height of flower stalks usually less than 4cm.|
Utricularia geoffrayi and U. minutissima were described in 1920 and 1806 respectively, an era where descriptions often lacked the depth of detail expected of modern publications. Taylor, in his 1989 monograph on ‘The Genus Utricularia’ systematically reviewed the genus and clarifies both species. While his examination of U. minutissima included material from Australia and across Asia, the material of U geoffrayi was limited to specimens from Indochina.
Taylor’s dichotomous key places emphasis on two characteristics for distinguishing the taxa: prominent veins on the calyx lobes of U. geoffrayi (veins indistinct on U. minutissima), and pedicels that are shorter than the surrounding bract in U. geoffrayi (the pedicels of U. minutissima are longer than the surrounding bract). While these traits are perhaps stable for specimens examined by Taylor in Indochina, it is apparent that it is not reliable for the species across its range. Under my observation, neither species have consistently raised calyx veins. Additionally, the length of the pedicel relative to the bract is a variable characteristic in Australian U. geoffrayi (Figure 5).
Lowrie in Magnum Opus (2013) updates and reviews both species within the Australian context. As Taylor only looked at Utricularia geoffrayi from Indochina and Lowrie focuses on the species as it appears in Australia, it is perhaps unsurprising that the two descriptions of that species differ in several traits. Lowrie notes that the peduncle in Australian U. geoffrayi is always covered with hispid indumenta, while they are glabrous under Taylor’s treatment. Personally, I’ve only found hispid indumenta in one of my photos (Figure 6). The spur in Australian plants is about twice as long as the lower corolla lip whereas the spur illustrated by Taylor just slightly protrudes from under the corolla lip (although spur length is not mentioned in Taylor’s text).
Lowrie’s key contradicts itself regarding the main diagnostic trait – the shape of the lower corolla lip margin. U. minutissima is simultaneously listed as having both three lobes and an entire/rounded/retuse margin (I think the intent was to say that U. geoffrayi is 3-lobed whereas U. minutissima is more shallowly so). Regardless, this trait is not the most useful under my observation with the corolla lobes of U. minutissima being similarly divided to U. geoffrayi in many examples. Lowrie’s secondary traits for identification focuses mainly on the colour of the bloom – purple and white with yellow eye dots in U. geoffrayi; and pink and white in U. minutissima. While colour is generally discouraged as an identifying trait owing to common natural variation and subjectivity in interpretation, it is undoubtedly useful in distinguishing these two taxa, at least in Australia (Figure 7). The truncated spur of U. minutissima (vs pointed in U. geoffrayi) is also listed and seems reliable for Australian plants.
To summarise, Utricularia geoffrayi and U. minutissima are variable taxa, both locally and throughout their geographic range. Descriptions of the plants might be accurate for plants in a certain area but may fail to fully match those in other locations. It is important to keep this morphological variation and limitations in published descriptions in mind when identifying these two closely related species.
Taylor, P. 1989. The genus Utricularia – a taxonomic monograph. Kew Bulletin Additional Series XIV: London.
Lowrie, A. 2013. Carnivorous Plants of Australia Magnum Opus – Volume One. Redfern Natural History Productions, Poole.