Aponogeton euryspermus [Adcock Gorge WA] - ©Dave Wilson


The genus Aponogeton is a group of freshwater aquatic plants belonging to the family Aponogetonaceae. The family consists of one genus with species occurring in Africa, Madagascar, India, South East Asia, New Guinea and Australia. The South African A. distachyos has been introduced to Australia (New South Wales, Victoria, South Australia). Aponogeton are popular aquarium plants and for many years they were collected from the wild. However, conservation measures introduced by Australian State Governments now restrict this practice. All species and naturally occurring hybrids of the genus are protected plants under the Queensland Nature Conservation Act. Members of the Aponogeton genus listed as threatened species in Queensland include A. bullosus (Endangered), A. prolifer (Endangered), A. cuneatus (Rare), A. queenslandicus (Rare) and A. elongatus subsp. elongatus (Rare).

Many specimens of Aponogeton from northern Australia were originally assigned to Aponogeton elongatus, but are now assigned to A. euryspermus, A. vanbruggenii or A. tofus. These species initially produce submerged leaves in flowing or clear water but later in the year plants often develop floating leaves. Species in this group can be separated by their seed shape and size; A. euryspermus has large broad seeds that can become very thick when mature, A. tofus has narrower almost cylindrical seeds, while A. vanbruggenii has even narrower seeds with a distinct knob at one end. All have seeds with an outer testa that is easily removed (thick in A. euryspermus and A. tofus - thin in A. vanbruggenii). All species are confined to the tropics with A. euryspermus more westerly in its distribution, A. vanbruggenii more easterly and A. tofus growing between the two but overlapping with A. vanbruggenii. A. tofus is closely related to A. euryspermus (as it had been previously identified); however, it is distinct and quite divergent at the molecular level from that and other species.

Most Aponogeton species produce a tuber and many, including some Australian species, go through an annual resting stage or dormancy period. Seasonal dormancy may be in response to wet and dry seasons, adverse environmental factors, low temperatures or drought. Under cultivation, in an aquarium, these plants often rot during the dormant period therefore aquarists commonly recommend removing the dormant plants from the aquarium and place them in moist media until growth recommences. However, a study by Crossley (2002) propagating and growing Aponogeton elongatus in a range of experiments provided no evidence of dormancy or a set rest period. One large plant, although not used in the study, had been actively growing for three and a half years in a display tank under 24 hours of continuous light. Plants were also observed to have abundant healthy foliage when collected from a creek in the middle of the winter. It appears that provided conditions are suitable these plants are capable of growing continuously without any ill effects.

Aponogeton bullosus - ©Glynn Aland

Aponogeton bullosus
Aponogeton bullosus is a tuberous perennial freshwater aquatic plant. The tubers take roots in the sand between stones in the streambed or in holes containing sand in larger boulders in the streambed. Leaf clusters emerge from the top of the tuber and are mostly submerged with a crinkled and bubbly appearance. The leaves are strap-shaped, tapered, translucent green or amber in colour. They are from 7 to 30 cm (sometimes to 50 cm) long and up to 2.5 cm wide and have distinctive veins. Leaves are tufted at the top of a tuber and may have a petiole up to 10 cm long though the petiole is usually shorter than this. Yellow flowers occur in a cone shaped spike borne at the top of a long slender peduncle that is from 8 to 30 cm long. The spike is usually submerged or just breaks the water surface. It is non-perfumed and up to 5 cm long and is subtended by a single bract up to 1.5 cm long. This species retains the bract longer than any other Australian species of Aponogeton. The bract usually remains attached to the lower portion of the spike although it is sometimes deciduous. The flowers sometimes emerge for a very short time above the surface for pollination and fall below the surface to develop fruit. Emergent flowers are not commonly seen. When the flowers do not emerge they still produce fruit. The infructescence is typically quite short, and conical with usually all fruit developed. The elongated fruit is 5 to 6 mm long and 3 to 4 mm wide and has a short beaked top. The distinguishing characteristic of this species is the extremely bullate leaves. Flowers and fruits from June to October. This species is a fully aquatic plant growing in cool rapidly flowing freshwater rivers and streams, in both sunny and shady positions.

Distribution: Aponogeton bullosus is known to occur between Tully and Cairns and west to the Ravenshoe area.

Aponogeton cuneatus - ©Craig McPherson

Aponogeton cuneatus
Aponogeton cuneatus is a tuberous perennial freshwater aquatic plant. Leaves are submersed and rarely floating; submersed blades narrow to broadly-elliptic to elongate, 10-50 cm long, 2-5 cm wide, green or dark green to maroon-green; margins sometimes slightly undulated. This species is named for the cuneate perianth segments characteristic of the species. Aponogeton cuneatus is distantly related to Aponogeton elongatus and actually most closely related to Aponogeton queenslandicus. A conspicuous difference exists in the shape of the perianth segments, with Aponogeton cuneatus having cuneate tepals (perianth segments) and Aponogeton elongatus having spathulate tepals. Grows in permanent creeks and rivers, often shaded.

Distribution: Aponogeton cuneatus is found in coastal north Queensland.

Aponogeton elongatus [Mary River QLD] - ©Gunther Schmida

Aponogeton elongatus
Submersed aquatic perennial. Leaves submersed and rarely floating (except for subsp. fluitans); submersed leaves green or dark green to maroon-green; margins slightly undulated.

Plants rarely or never producing floating leaves ..... subsp. elongatus

Plants commonly producing floating leaves ..... subsp. fluitans

Aponogeton elongatus subsp. elongatus
Coastal Queensland and coastal northeastern New South Wales. Grows in freshwater portion of coastal rivers and streams. Flowers and fruits from October to March.

Aponogeton elongatus subsp. fluitans
Localised in creeks and streams in parts of south-east Queensland. Grows in freshwater rivers and streams through rainforest. Flowers and fruits from October through April. This subspecies is named for the distinctive floating leaves; from the Latin fluito, float. This subspecies might be mistaken for the tropical species A. euryspermus or A. vanbruggenii. Aponogeton elongatus subsp. fluitans is easily distinguished from the other two taxa by the distinctive seed shape and coat. All three may produce floating leaves.

Aponogeton euryspermus [Adcock Gorge WA] - ©Franz-Peter Muellenholz

Aponogeton euryspermus
Submersed aquatic perennial. Leaves submersed and/or floating. Submersed leaves linear, linear-lanceolate, ovate, or elliptic, to 23-35 cm long, 0.5-6 cm wide; margins flat or slightly undulated. Floating leaves ovate or elliptic, to 11 cm long, green to maroon. Inflorescence yellow, emergent or floating, single, rarely branched, to c. 17 cm long. This species is named for the large broad seed produced; from the Greek eurys, broad and spermus, seed. Grows in freshwater streams, rivers and lagoons. Flowering and fruiting December to February and May to July.

Distribution: Northern portion of Western Australia from the Kimberley east to the northern portion of the Northern Territory and Arnhem Land.

Aponogeton hexatepalus
Submerged and floating aquatic perennial. Leaves floating, narrowly oblong, to 20 cm long, 0.3-0.7 cm wide. Inflorescence branched forming 2 spikes, green (yellowish-green), to 17 cm long. Grows in freshwater ephemeral pools that contain water for 3 to 4 months a year. Flowering and fruiting from August to November. This is the only species of Aponogeton that consistently has 6 perianth segments.

Distribution: Endemic to southwest Western Australia in the vicinity of Perth. Now rare due to loss of habitat.

Aponogeton kimberleyensis
Submerged aquatic perennial. Leaves submersed; blades linear, rarely slightly broadened, 24-32 cm long, 0.09-0.3 cm wide; dark green; margins flat; base longtapered. Inflorescence yellow, emergent, single, to 7.5 cm long. Flowering and fruiting specimens from March and May.

Distribution: Endemic to the western Kimberley region in Western Australia.

Aponogeton lancesmithii
Submerged aquatic perennial. Leaves submersed; blades linear-lanceolate, 10-48 cm long 0.9-4 cm wide, slightly to strongly bullate, green to dark green; margins slightly undulated. Inflorescence yellow, often floating on surface with the tip emergent, single, rarely branched, to c. 34 cm long, sparsely to tightly flowered. Flowers and Fruits from at least July to November. Unlike A. bullosus, which produces fairly short peduncles and mostly submerged inflorescences, A. lancesmithii produces very long inflorescences on inflated peduncles that are longer than any other species in Australia. The inflorescences are usually emergent. The leaves are often bullate. This species is named for Lance Smith, an aquatic plant propagator and grower from Kelso (Townsville), Queensland.

Distribution: Endemic to the Russell River and its tributaries in the Innisfail District of Far Northern Queensland.

Aponogeton prolifer
Aponogeton prolifer, formerly known as Aponogeton proliferus, is a rooted, submerged, perennial aquatic. Tubers are small, less than 1 cm long. Leaves are submersed, 18-31 cm long, and usually 1.3-1.6 cm wide. The yellow flower head is emergent, up to 5.5 cm long on stalks that grow to 32 cm long. The spathe (leaf like structure that protects the inflorescence) grows to 1.5 cm long. New plants are commonly produced at the tip of inflorescence-like structures and these proliferous shoots distinguish the species. This species is named for the proliferous shoots produced; from the Latin prolifer. Despite the proliferous shoots this species is difficult to propagate and the proliferous offshoots need to remain in contact with the parent plant until well established. This is the only yellow-flowered taxon of two proliferous species known worldwide. The other is Aponogeton undulatus, a white-flowered species from Asia.

Distribution: Aponogeton prolifer is known only from creeks running through rainforest margins in the Innisfail region, northern Queensland. It occurs in narrow, shallow and heavily shaded coastal streams. Presumably now restricted because of extensive clearing and loss of habitat.

Aponogeton queenslandicus - photo© Bruce Hansen

Aponogeton queenslandicus
Aponogeton queenslandicus is a seasonally emergent aquatic plant with a tuberous base supporting leaves, which are nearly always surface floating, and flowering spikes, which are shortly emergent above the water surface. Grows in freshwater ephemeral habitats in drier regions, ponds, and roadside ditches. Flowers and fruits in response to water levels and temperature, but more commonly during the warmer months. The leaves are surface floating, firm, green and oval with a rounded or heart-shaped base and a somewhat narrowed tip. They are from 5 to 11 cm long and 1 to 3 cm across, and borne on slender petioles 5 to 25 cm long. There are 5 to 7 distinct veins running along the leaf blade. The inflorescence is a tapering; cylindrical, yellowish spike up to 9 cm long subtended by a short bract about 1.5 cm long at the base. This bract usually falls early. The small flowers are densely packed on the spike. Flowering January to September. The fruit are crowded on the stem, are about 8 mm long and 5 mm across and have a short curved beak on the top. Aponogeton queenslandicus occasionally produces submersed leaves.

Distribution: North-east Northern Territory and throughout Queensland south of Cape York Peninsula, though more common west of the Great Divide but uncommon in the driest areas.

Aponogeton tofus - photo© Dave Wilson

Aponogeton tofus
Submersed aquatic perennial. Leaves mostly submersed, sometimes floating. Submersed blades linear, linear-lanceolate, ovate, or elliptic, to 23-35 cm long, 0.5-6 cm wide; margins flat or slightly undulated. Floating leaves ovate or elliptic, to 11 cm long, green to maroon; margins flat. Inflorescence yellow, emergent or floating, single, rarely branched, to c. 17 cm long. Grows in freshwater streams, rivers and lagoons, usually in or near sandstone country, especially the Arnhem Land Plateau. Flowering and fruiting December to February and May to July.

Distribution: Northern portion of the Northern Territory and Arnhem Land.

Aponogeton vanbruggenii - ©Dave Wilson

Aponogeton vanbruggenii
Submersed aquatic perennial. Leaves submerged and/or floating. Submersed blades lanceolate, elliptic, or obovate, 7-36 cm long, 0.6-5 cm wide, green to maroon; margins slightly to strongly undulated. Inflorescence yellow, emergent or floating, single, tightly flowered to widely spaced along rachis. Grows in freshwater rivers, streams, still-water portions of lakes, and billabongs. Flowers and fruits recorded from March to October and January. Aponogeton vanbruggenii superficially resembles Aponogeton euryspermus but differs from that species in having smaller and narrower seed with a distinct knob at one end. Aponogeton vanbruggenii, like Aponogeton euryspermus, also may regularly produce floating leaves in still or turbid waters, especially late in the season. A few populations of Aponogeton vanbruggenii appear very similar to Aponogeton queenslandicus, with mainly floating leaves, but the two species are easily distinguished by the seeds.

Distribution: Eastern tropical Northern Territory and Queensland.

Hellquist C. B. and S.W. L. Jacobs (1998) Aponogetonaceae of Australia, with descriptions of six new taxa. Telopea Volume 8(1): 7-19.

Adrian R. Tappin
January, 2011

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