Senegal tea plant is on the Alert List for
Environmental Weeds, a list of 28 nonnative
plants that threaten biodiversity
and cause other environmental damage.
Although only in the early stages of
establishment, these weeds have the
potential to seriously degrade Australia’s
ecosystems.
Senegal tea plant can float on still or very
slow-moving fresh water or grow as a
bush on wet, marshy soils. It has been
recorded at localised sites in most states.
It is mainly spread by the careless disposal
of aquarium plants or deliberate
cultivation for sale.
Because Senegal tea plant grows very
quickly, it can rapidly cover water bodies
with a floating mat, excluding other
plants and the animals that rely on them.
The effects of flooding are made much
worse because infestations block drainage
channels. Recreational activities, irrigation
and navigation may also be affected.
Water quality may decline if large
amounts of Senegal tea plant die off
and rot under water.
Senegal tea plant can grow as an erect,
rounded bush up to 1 m tall, but is more
commonly found as a scrambling form
extending from the edges of waterways
and forming dense tangled mats in open
water. Young stems are 5–10 mm in
diameter, increasing to 20 mm with age.
Larger stems are hollow between the
nodes (the joints between segments of
stem) and float on water, and can reach
a length of 1.5 m. The leaves are dark
green, 50–200 mm long and arranged
in opposite pairs along the stem. The
edges of the spearhead-shaped leaves
are serrated.
The numerous, white, ball-shaped
flowers, 15–20 mm in diameter, occur
at the ends of stems. The ribbed seeds
are yellow–brown and 5 mm in diameter.
Thin, fibrous roots can develop at any
node that is in contact with moist soil
or immersed in water.
Senegal tea plant can reproduce by seeds
and vegetation. The seeds are quite heavy
and most drop near the parent plant or
can be spread by flowing water. Seeds
can also be spread in mud attached to
animals or machinery. Recent research
has shown that seed production in
infestations near Brisbane is extremely
low, less than 1% of its potential, which
indicates that spread of Senegal tea plant
by seed is not very important there.
Vegetative spread occurs when any part
of the stem that includes a node breaks
away from the main plant, eg in fast
flowing water. When the stem fragment
settles on the stream bed it sends out
fine roots from the node, and can grow
into an entire new plant. This new plant
can spread quickly and create a colony
by producing roots where nodes come
in contact with moist soil. Stem fragments
can also be accidentally spread by
transport of machinery (eg boats, trailers,
lawnmowers) or in animals’ hooves.
Senegal tea plant was introduced into
Australia from India by the aquarium
industry. It was first recorded as growing
in the wild in the Manning River near
Taree, New South Wales, in 1980. Several
other infestations have been recorded
throughout New South Wales and Tasmania,
with more recent spread recorded
at several sites in and around Brisbane.
Infestations were recently recorded from
Perth and at Lake Nagambie and
Cranbourne South in Victoria.
Senegal tea plant grows in wetlands,
particularly degraded waterways. It can
flourish in still or slow-moving fresh water,
rooted in the bank and floating out into
the waterway. It survives and continues
growing even when completely inundated.
It also grows on wet marshy soils
near water.
Senegal tea plant grows very quickly in
fertile environments, with growth rates
exceeding 150 mm a week.
It is a native of tropical and subtropical
regions of the Americas, from Mexico
to Argentina, where it has also been
recorded as a weed. New Zealand and
India are other countries where it has
become weedy.