The Tillandsia genus can be separated into seven different subgenera. In taxonomic rank, subgenus sits above species and below genus. Simply put, this is another way to group similar plants together. Plants within a subgenus will have similar-looking flowers and will be able to reproduce together. Scientists use the flower and flower parts to identify subgenera (and plant species!) because the reproductive parts of plants are the oldest and the slowest to evolve- these are the most "stable" identifying plant parts. We use subgenera to group species together for various reasons- two plants may or may not hybridize together, for example, based on their subgenera. Plants within a subgenera are not necessarily native to the same geographic areas, but they will be closely related, genetically. By studying which plants belong to which subgenera and by looking at flower parts, it may eventually be possible for you to identify an unknown species' subgenus by sight alone, and by extension to know other qualities about the unknown species.
A Type species is the designated "standard" of a subgenus and acts as an example . Historically, the type species were recorded as real plant specimens housed in a recognized herbarium- these were the original plants used to describe a subgenus. These example plants help us to use plant names effectively and consistently. The seven subgenera and their type specimens are listed below.
Subgenus Tillandsia is known for its purple, tubular flowers. This subgenus holds many popular and easy-to-grow species. Most Tillandsia that are native to the the United States are contained here. Subgenus Tillandsia holds about 125 species, native from the southeastern United States down into Central America.
Plants of subgenus Tillandsia:
T. utriculata (photo credit: Scott Zona)
Allardtia holds about 147 (the most of any Tillandsia subgenus) species native from Mexico down to Central America, the Caribbean, and some parts of South America. To identify this subgenus, it is necessary to dissect a flower.
Plants of subgenus Allardtia:
T. guatemalensis (photo credit: Derek Butcher wwww.bromeliad.org.au)
This subgenus holds about 30 species which are known for their spectacular and fragrant flowers. These plants are native from Nicaragua down through South America. Many of the plants within this group come from xeric conditions, and their flowers are typically fragrant to support their chief pollinators: moths. This also means that many of the plants in Phytarrhiza bloom for only a short time, and at night.
Plants of subgenus Phytarrhiza:
T. duratii (photo credit Paul T. Isley III)
Diaphoranthema contains about 16 species, with the largest native range by far of any Tillandsia subgenus, possibly due to the help of birds. These plants are known for being self-pollinators, so they will easily reproduce, but their flowers are typically small and simple, as the pollen is created deep within the flower. These species are known as the miniature Tillandsia and they often grow in chains and clump easily.
Plants of subgenus Diaphoranthema:
T. recurvata (photo credit: www.airplanthub.com)
Anoplophytum contains about 30 species and must be distinguished from Allardtia by dissecting the flower. This group holds many different popular plants that generally enjoy more-humid environments.
Plants of subgenus Anoplophytum:
T. stricta (photo credit: Paul T. Isley III)
Containing only four species, this group contains all mesic plants in a rosette shape. No less beautiful or amazing than any other Tillandsia, these are rarely seen in collections.
Plants of subgenus Pseudalcantarea:
T. viridifolia (photo credit: Timm Stolten)
Currently, most of the previous members of Tillandsia subgenus Pseudo-Catopsis have been moved into the newly-created genus Racinaea- these are technically no longer Tillandsia. Previously, 21 species existed in Pseudo-Catopsis, but only T. fraseri was widely available.
Plants of subgenus Pseudo-Catopsis: scientific rearrangement ongoing.
T. fraseri, now known as Racinaea fraseri (photo credit: Andreas Kay)