is a genus of plants in the grass family, found in coastal salt marshes at many places around the world. Its photosynthesis uses C4 carbon fixation which may be more efficient than the normal C3 version and this allows it to resist conditions of water stress.
, the small cordgrass
, smooth cordgrass, showing its growth habit along the edges of a saltmarsh creek
In Southampton water (UK) in about 1870 the native species Spartina maritima
) hybridised with the introduced American species Spartina alterniflora
(possibly originally introduced in ships' ballast water).
The resulting plants were given the name Spartina × townsendii
. These plants were infertile, and could not cross with either parent. However they could reproduce asexually and established a colony that is still visible today near Hythe.
It was found that in about 1890 (some of) the hybrid had doubled its chromosome number, possibly as a result of problems in cell division, with the result that a new ('allotetraploid') species Spartina anglica
had been formed. This is fertile, as each chromosome can pair with the extra copy of itself when undergoing meiosis to produce gametes. Spartina anglica
can set seed and has established itself naturally at several locations along the coast. It has also been introduced by Man at various sites around the world, mostly in schemes to stabilise coastland against tidal erosion.
is much more vigorous than the parental types and has developed into an invasive species in several parts of the world. It grows densely and does not support much invertebrate life, nor does it lend itself as a habitat to wildfowl.
has hybridised with other species of Spartina
and has been studied extensively to determine the genetic basis for its competitiveness. It has been found that its genome has been significantly epigenetically modified by methylation.
A recent discovery
Monkeyflowers is the name given to a number of plant species which are quite popular garden flowers. They used to be placed in the genus Mimulus
, but they have been reclassified into the genus Erythranthe
. They mostly originate from North America, but several ('escaped') populations have become established in the United Kingdom, mainly in Northern England and Scotland.
This is a colony of hybrid monkeyflower Erythranthe × robertsii
growing alongside a stream in Dovedale, Derbyshire
This is the flower of Erythranthe peregrina
In 2011 a new species was recorded (although it might have formed in the last 140 years):
originated from E. × robertsii
, a sterile hybrid between E. guttata
and E. lutea
Palms of Lord Howe Island
Lord Howe Island (600km east of western Australia, and 1880 km north west of New Zealand North Island) has a subtropical climate.
This island - with an area of 14.55 km2
- formed 6.9 million years ago as a result of volcanic activity.
It has two raised rocky peaks, the remnants of a volcano crater, and well vegetated lower ground.
Four species of palm tree are endemic to it.
These include two closely related species : Howea forsteriana
and H. belmoreana
- also known as Kentia palms - which have been studied and found to result from sympatric speciation.
(Kentia Palm or Thatch palm) - up to 10 m tall by 6 m wide. Its fronds can reach 3 m long
(Belmore sentry palm) - canopy 2–3 m in diameter, containing roughly 36 leaves.
These have evolved from a common ancestor, which presumably must have originated from another island. The initial colonisation may have resulted from a seed washed up on the beach which germinated and grew into a mature tree, and was self-fertile and so could reproduce sexually. This could then give rise to a number of similar but genetically variable palm trees along the shoreline. Seed dispersal by animals (birds?) or weather action would extend the distribution inland.
It is conceivable that a gene/allele causing later flowering could have occurred as a result of a mutation. Several examples of epistatic late-flowering genes are known in well-studied plants such as Arabidopsis thaliana
There are areas of the island with different soil types and microclimates and it has been suggested that these differences could act as drivers of parapatric speciation..
Plants growing on calcareous sandy soils - derived from weathered corals - in the lower regions of the island are more likely to experience shortage of certain minerals whereas those growing on richer basaltic soils resulting from volcanic lava flows of the higher regions do not suffer from this disadvantage. This tends to favour earlier flowering on the lower parts of the island, whereas the plants growing in higher regions can grow more steadily and flower later. As late-flowering plants are at a disadvantage in the lower regions, and early-flowering plants are not at an advantage in the higher regions, a form of disruptive natural selection takes place.
Although both species do exist alongside one another in places, H. forsteriana
is more common in the lowland which has sandy calcareous soil. It flowers six or seven weeks earlier than H. belmoreana
which is quite abundant at higher elevations (up to 450 metres) where the soil is neutral/acidic. Numerically there are more specimens of H. belmoreana
on the island, competing with a variety of other plants in the inland forest, and more young plants, so the popuation has not yet climaxed.
These palms are wind pollinated and produce large amounts of pollen at different times of the year, which causes genetic isolation, so that allele frequencies can be expected to differ in the two populations. The two species differ in height and the shape of their leaf fronds, H. forsteriana
being more droopy and H. belmoreana
A few examples of hybrids between the two Howea
species exist, but it is not known if they set seed.
These palm trees have been exported to other parts of the world and have been quite popular horticulturally in Europe - originally in Palm Courts of Victorian and Georgian hotels, and commercial plantations have been established on other islands e.g. Norfolk Island. They are also popular as smaller plants in modern houses.
In previous times, their seeds/fruit were used as a food by passing sailors.