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Gesneriaceae occupy an
extremely wide range of habitats. The altitudinal range is from sea level to
nearly 5000 m (Corallodiscus kingianus). Therefore, it is not
easy to identify special and limiting ecophysiological factors for the
family. One factor seems important for almost all Gesneriaceae, irrespective
of habitat type: high humidity, necessary either throughout the year or at
least in distinctive growing periods.
At low altitudes,
gesneriads are predominantly bound to forest habitats, growing in damp,
shady places on slopes or moist rocks, often nearby streams or waterfalls.
In the equatorial rain forests of Asia there are relatively few gesneriads
in the lowlands (e.g., Cyrtandra, some species of Henckelia,
and rock plants such as Monophyllaea, Epithema, Paraboea
etc.), but they abound in the montane forests with their cool and ever-moist
conditions. This distribution is mirrored in the neotropics, with few
species occurring in the lowlands, e.g., Amazon basin, but abounding in the
Andean uplands. More open habitats are rocky, damp and humid gorges, the
home of many Streptocarpus species in South Africa. Also in alpine
habitats (Himalayas, South China, Pyrenees), the plants grow usually in open
habitats, but seem to be generally restricted to shady humid places such as
rock crevices, overhanging rocks, shallow caves and cave entrances.
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Terrestrial Gesneriaceae
growing under constantly warm and moist conditions are not in need of
special morphological and/or ecophysiological devices. Plants
living in areas and habitats with periodically changing climate (especially
amount of precipitation), however, had to develop special adaptations and
survival strategies, restricting growth and flowering to a short period of
favourable conditions. Morphologically, these adaptations include: annual
habit, development of seasonal shoots, underground storage organs such as
rhizomes, scaly rhizomes and tubers in many neotropical Gesneriaceae, and leaf abscission
in Streptocarpus (see
the previous sections Life Forms and Growth Patterns and
Exceptional Morphologies).
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Physiologically, the most
remarkable feature of many Gesneriaceae is their capability to survive
periodical desiccation. In the dry period the leaves shrivel and the plants
look dead. However, when moist conditions return, the plants recover fully.
Thus they are also called “resurrection plants“. Some species
have been named after this ability: the Chinese Boea hygrometrica,
the Australian Boea hygroscopica and the Madagascan Streptocarpus
revivescens. The European gesneriads Ramonda, Haberlea and
Jancaea also are resurrection plants, and most probably species of
Corallodiscus, Paraboea, Trisepalum, Henckelia sect. Henckelia
and others can be added. Desiccation survival is also facilitated in some
species by fleshy succulent leaves (e.g. species of
Codonanthe,
Nematanthus, Aeschynanthus, Columnea, etc.). |
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