Fasciation
Lew Feldman, Director
Fasciation is a condition in which the tip of a shoot or flower, instead of producing a cylindrical axis that elongates, produces flattened, elongated and often contorted parts. This abnormal growth pattern is sometimes referred to as “crested.”
An example at the Garden that intrigues visitors – from school children to adults – is the Madagascar palm (not a palm at all), Pachypodium lamerei, found in the Arid House. A stem succulent native to Madagascar, this plant photosynthesizes mainly through its trunk. But like many fasciated plants, it has taken on a bizarre shape completely unlike its normal form.
Pachypodium lamerei
The term fasciation comes from the Latin fascis, meaning bundle; fasciated plant parts often look like they have been flattened and stacked together. Many collectors value these rare oddities, which are believed to arise because of abnormal changes in the levels of plant growth regulators (hormones; probably cytokinins and auxins). A number of explanations have been advanced for these hormonal imbalances, including natural mutations, bacterial and viral infections, and insect and mite infestations. It has also been reported that cold (including frost) can cause fasciation, probably by damaging the normally rapidly dividing cells at the tip of the affected plant part.
Although not common here in the Garden, fasciation does occur occasionally in other plants, with perhaps the most notable example being fasciation of the inflorescence of an indigo plant (Indigofera pseudotinctoria), located in the Herb Garden.
The UC Agriculture and Natural Resources IPM (Integrated Pest Management) website notes that if the underlying cause of fasciation in a particular plant is bacterial or viral, this may affect the health of the plant and lead to premature death. They advise that to “control fasciation due to all likely causes (genetic and microbial), prune off and dispose of distorted tissue [and] do not propagate or graft symptomatic plants.”
Some fasciated plants are given cultivar or varietal names such as “monstrosa” or “tortulosa,” but many horticulturists and ordinary gardeners appreciate the unique beauty of this unusual growth. In fact, the UK Royal Horticultural Society names several plants that are prized and propagated for their fasciated forms. Plants in which the fasciation is not genetic, such as the willow Salix udensis ‘Sekka,’ can be propagated from cuttings. Cockscomb, Celosia argentea var. critsata is a “cristate” (crested) horticultural variety in which the fasciation is genetic, so these plants are propagated from seeds.
Top Image: Indigo plant (Indigofera pseudotinctoria) inflorescence, Herb Garden.