| Gesnerioideae |
Sinningia, Columnea, Nematanthus, Achimenes, Episcia, Gesneria, Drymonia |
South and Central America, Caribbean islands |
Symmetrical cotyledons,
3-DAs,
some genera with inferior or partially inferior ovaries |
1400 |
| Cyrtandroideae |
Saintpaulia, Streptocarpus, Chirita, Aeschynanthus, Cyrtandra, Petrocosmea |
South Africa, Southeast Asia, Pacific Islands |
Asymmetrical cotyledons, superior ovaries |
1800 |
The Western Hemisphere gesneriads almost all belong to the Gesnerioideae.
They have symmetrical cotyledons,
unlike the Cyrtandroideae.
Most of them are pollinated by hummingbirds, and others are pollinated by
euglossine bees.
A special pigment type
(3-deoxyanthocyanins)
is found in most genera of this subfamily.
These pigments are bright red or yellow, and are associated with
hummingbird pollination.
The Gesnerieae tribe (Gesneria, Rhytidophyllum) is found mostly on the islands
of the Caribbean.
The Sinningieae tribe is found mostly in Brazil.
Other gesnerioid tribes are found in Mexico, Central America, and
northern South America.
Underground storage organs, like scaly rhizomes and tubers, are found in a
number of genera of the Gesnerioideae.
Recently, it has been proposed that the genus Titanotrichum, from Taiwan and
eastern mainland China, is actually a member of the Gesnerioideae.
The largest subfamily of the Gesneriaceae is confined to the eastern hemisphere.
(At least, it is if the proposed segregation of the tribe Klugieae into a separate
subfamily is followed - see below.)
It has two centers of concentration: South Africa and Madagascar (Saintpaulia
and Streptocarpus) and Southeast Asia (all other genera).
The Cyrtandroideae are characterized by the
accrescent cotyledon.
This subfamily includes two of the youngest and fastest-growing genera of
the family: Cyrtandra and Aeschynanthus.
Possession of berry fruit has allowed Cyrtandra to colonize the (geologically
young) islands of the Pacific.
It may be that the hairy seeds of Aeschynanthus also contribute to its dispersal
through the South Pacific (over a range not as large as that of Cyrtandra).
Many (most?) aeschynanthus are pollinated by birds, although not by hummingbirds,
since hummingbirds are confined to the western hemisphere.
There is one character found in a couple of widely separated genera of this
subfamily.
Streptocarpus and Boea have long fruits which are spirally twisted.
This may be an innovation to facilitate seed dispersal.
When the fruit is ripe, it splits open and untwists, releasing the seeds gradually.
Since Boea and Streptocarpus are not close geographically, it is likely that they
evolved this trait separately.
The late Hans Wiehler split off the tribe Coronanthereae
from the Gesnerioideae into a
separate subfamily, the Coronantheroideae.
Since Sarmienta and Mitraria share a special
pigment
(3-deoxyanthocyanins)
with the Gesnerioideae, the chemical evidence
suggests that the Coronantheroideae might perhaps be an
entity multiplied without necessity.
Coronantheroids are native to the Pacific coast of Chile (Sarmienta,
Mitraria, Asteranthera) and islands of the South Pacific (Fieldia, Negria, Rhabdothamnus).
Just recently, it has been proposed that the tribe Klugieae, comprising a few
species of unusual gesneriads, be removed from the Cyrtandroideae to its own
subfamily.
The largest genus in the tribe is (I believe) Monophyllaea, with perhaps 30 species.
This tribe also includes one species, Rhynchoglossum
notonianum, found in Central America.
How it got there, nobody knows, since the species does not have a fruit
designed for long-range dispersal.