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Specimen count
Pteridophyte taxa known or reported from Sulawesi
Lecanopteris spinosa
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Life cycle
In common with other ferns, Lecanopteris has 2 alternating generations. These are the:
- sporophyte generation - the main fern plant that produces spores inside sporangia
- gametophyte generation - a small insignificant prothallus that develops from a germinating spore
Male and female sex organs are produced on the gametophyte and fertilisation takes place when there is sufficient moisture, usually between different individuals. The resultant zygote grows into a new sporophyte plant.
Dispersal
In Lecanopteris spinosa and some other Lecanopteris species, spores are shed in clusters of 4, connected by the flaky spore surface. This is unusual in ferns and may be an adaptation to the ant - fern association.
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Rights holder/Author | Alison Paul, Natural History Museum |
Source | No source database. |
Ant - fern association
All species of Lecanopteris have greatly modified rhizomes that form hollow chambers in which ants nest and raise their broods.Although it is rare to find Lecanopteris plants with ant-free domatia, the relationship between Lecanopteris and the ants is facultative rather than obligatory. Each partner can survive without the other, though possibly survival and vigour of the plants may be affected in the absence of ants. Although the ants are not dependent on the rhizomes for nesting, they will take advantage of them whenever they are available.
Benefits to the plant
Lecanopteris plants gain nutrients and water from ants. This happens in several ways:
- ants bring into the rhizome organic matter and debris that decomposes along with their faeces and corpses, providing water and nutrients such as nitrogen that the fern can absorb through the inner rhizome walls - this method of nutrient uptake in Lecanopteris is different from that in other ant-epiphytes as there are no specialised absorptive structures within the domatium.
- in Lecanopteris spinosa, the solutes can also be taken up via roots that have penetrated the cavities - probably through old decayed leaf bases - and developed abundant root hairs.
- the fern roots on the surface of the tree branch can absorb nutrients from the carton of ‘carton runways’, continuous tunnels on the host tree trunk and branches built by ants from chewed plant material cemented with saliva. These runways allow the ants to leave the host plant safely whilst foraging on the tree, but have not been observed in association with L. spinosa.
Plants may in some cases receive protection from being eaten by insects or animals. Crematogaster are small, non-stinging ants that could see disturbance as a threat to their nests and attack when disturbed. There is, however, evidence that they do not always perform this service.Ants probably assist spore dispersal incidentally while they are foraging.
Benefits to the ants
Ants have the benefit of a sheltered safe place to nest and rear their larvae. For an ant colony to thrive, cool, dry and dark conditions are needed. The hollow Lecanopteris rhizome forms a domatium (home) that provides these as:
- the rhizome chambers are dark inside
- the thick waxy epidermis and stomata-less rhizome help prevent excessive water loss and dehydration
- the internal walls of the domatia need to be moist but not wet to avoid fungal or bacterial attack - excess moisture is removed by the internal absorptive surface, so the larvae are protected from rotting
- the thick rhizomes buffer the nest and protect larvae from the high temperatures that could occur since they are sun epiphytes
Ants are found in succulent green rhizomes as well as old blackened ones and probably gain water and nutrients from the plant.It has been reported that in some Lecanopteris species oil droplets produced in the sporangia may be harvested by ants as a source of food.In studies of 7 Lecanopteris species, over 30 species of ants were recorded as visiting the plants, 5 of which were ‘regulars’. These were:
- Crematogaster treubi
- Crematogaster difformis
- Camponotus pallidus
- Iridomyrmex cordatus
- Iridomyrmex murinus
Within a population of Lecanopteris, or a particular geographic area or habitat, ants tend to associate with specific species. The same species of ant will colonise most Lecanopteris plants in a population throughout the life of the plants. As long as at least a small portion of the plant is living it will be inhabited by ants but totally dead plants are deserted. Studies of other species of Lecanopteris have shown that the relationship between ants and ferns is a result of ecology not of co-evolution - when a Lecanopteris species is distributed more widely than the ants, another species of ant takes its place. Not surprisingly, the greatest range of ant species was found in the most widespread fern species, Lecanopteris sinuosa. A single ant species will colonise a range of different ant-epiphytes.Lecanopteris spinosa was not investigated in that study but ants of the genus Crematogaster were found in L. spinosa rhizomes when they were originally collected and were deposited in the Museum's Entomology collections.
License | http://creativecommons.org/licenses/by-nc-sa/3.0/ |
Rights holder/Author | Alison Paul, Natural History Museum |
Source | No source database. |
Lecanopteris is almost exclusively a Malesian genus, with only 1 species extending into other parts of south-east Asia and just reaching Queensland and Vanuatu. Sulawesi in Indonesia is the centre of distribution - of the 13 known species, 8 occur in Sulawesi. 6 of these are endemic, of which 5 have a very restricted distribution and are only known from a few collections. More extensive exploration could reveal other populations.Lecanopteris spinosa has only been found on Mount Rantemario in the Latimojong Mountains of south Sulawesi at roughly 1,950m altitude.
Ecology
Lecanopteris species:
- are epiphytes and derive nutrients from accumulated organic matter and rainfall; they are not parasitic
- seem to have no preference for particular host tree species
- often grow on trees with rough bark
- are sun epiphytes, growing on exposed branches with high light levels
- all develop rhizome domatia that shelter ants
Lecanopteris spinosa:
- is a high epiphyte in undisturbed open mixed oak-podocarp forest (upper montane evergreen forest)
- is found on upper branches - 3 to 6cm thick - of Platea latifolia trees 15 to 30m high
License | http://creativecommons.org/licenses/by-nc-sa/3.0/ |
Rights holder/Author | Alison Paul, Natural History Museum |
Source | No source database. |
Lecanopteris is in the large global family, Polypodiaceae. 13 species of Lecanopteris are currently recognised.Lecanopteris has been split by some researchers into 2 genera (or into 2 sections of Lecanopteris) on the basis of 2 main features:
- Myrmecopteris has
- rhizome clothed with distinctive scales
- sori (clusters of spore capsules) that are not marginal
- Lecanopteris has
- rhizome that is not scaly
- sori on reflexed marginal lobes of the frond
L. spinosa is intermediate between these 2 groups, having no scales but with sori not marginal. Thus its discovery supported the recognition of a single genus.Subsequent research suggested that since Myrmecopteris seemed to be closely related to the genus Phymatodes, Lecanopteris in the broad sense could not be monophyletic and the 2 subgenera might have had different origins. However, more recent DNA studies support Lecanopteris as a monophyletic genus comprising closely related species derived from a common ancestor.
Morphology
In Lecanopteris spinosa the rhizome is:
- creeping and much branched
- 2.5 to 4.0cm in diameter
- pale green and glaucous when young, becoming black with age and without stomata
- grows continuously and dies back at the other end
- grows in 3 to 4 superimposed layers around a branch to form a ball-like clump up to 25cm across
- densely covered with strong spines up to 6mm long
- glabrous - lacks scales or hairs except when very young
- hollow - as it ages the pith cells in the centre dry out and shrink to form cavities exploited by ants
The morphology and internal structure of the rhizome varies in complexity according to the species. Most have a single gallery running through the rhizome and into the side branches but a few, including Lecanopteris spinosa, have a much more complex system of interconnecting galleries and chambers.The fronds are:
- simple (sterile fronds) or lobed (fertile fronds)
- more-or-less sessile (not stalked)
- jointed to rhizome
- lamina (leaf blade) up to 30cm long and 3 to 4cm wide
- leathery
- glabrous
The sori are:
- round
- in 1 row on either side of the rachis (midrib)
- deeply immersed in the frond so they project on the upper surface
- naked, having no protective indusium - a characteristic of the Polypodiaceae
Look-alikes
Lecanopteris spinosa is unlikely to be confused with other species of Lecanopteris due to its unique combination of characters:
- rhizome forms ball-like clumps
- rhizome has many rigid spines but no scales
- fronds are simple or lobed
- sori are sunken and in 1 row on either side of the rachis
License | http://creativecommons.org/licenses/by-nc-sa/3.0/ |
Rights holder/Author | Alison Paul, Natural History Museum |
Source | No source database. |
Ant-ferns are intriguing plants that have developed a mutually beneficial relationship with ants, whereby:
- ants provide nutrients for the plant
- the plant provides shelter for the ants to live and raise their broods
Lecanopteris spinosa was discovered by Clive Jermy - Head of the Fern Section at the Natural History Museum for many years - and his colleague Trevor Walker from the University of Newcastle-upon-Tyne during an expedition to Sulawesi in 1979. It is still known only from this locality.The discovery of this species helped to resolve the differences of opinion as to whether to recognise 1 or 2 genera of Old World ant-ferns.
License | http://creativecommons.org/licenses/by-nc-sa/3.0/ |
Rights holder/Author | Alison Paul, Natural History Museum |
Source | No source database. |