Merremia is the largest of the 10 genera in the tribe Merremieae in Family Convolvulaceae.
Classification of Merremieae is an ongoing work as its members do not have a single common
ancestor and no single common feature to unite them all.
It could be considered to consist of a lot of species that just do not fit into the other genera.
It is seen as a loosely defined genus Merremia s.l. with around 100 species and a
strictly defined one Merremia s.s with around 50 species.
Mabberley recognises around 100 species.
Features used to separate the 2 include the presence or absence of a coloured spot at the base of
the petals and the sepal lobes being blunt or pointed.
Merremia are very difficult to separate from Ipomoea with many species having been in both genera
as well as in the Convolvulus genus.
Smooth or spiny pollen is the only way to distinguish some Merremia and Ipomoea.
Merremia are widespread throughout the tropics with the origin of many being uncertain.
Most are vines that are prostrate or climb by twining but there are also a few small erect shrubs.
The vines can be up to 30 m long.
The alternate leaves, up to 30 or 40 cm long can be simple, variously lobed or compound.
Inflorescences are a single axillary flower or a few in a branched cluster.
There may be 2 bracts at the base of the peduncle.
Flowers, up to 6 cm long are mostly white but there are some yellow ones.
The 5 sepals are usually of unequal length.
The 5 petals are fused into a bell or funnel-shaped corolla with a smooth or lobed edge.
Dark veins run down the centre of the petals and their base may be purple or red.
The hairless corolla may be swollen on one side.
The 5 stamens insert onto the corolla tube.
The anthers open longitudinally and the tips may be curved or twisted.
The pollen is smooth.
The superior ovary is mostly hairless.
It has 2 locules with 2 ovules in each but septa usually divided it into 4 locules holding 1 ovule.
There is a single style with a 2-lobed stigma.
The fruit are capsules with one seed in each of the 4 chambers.
The sepals remain attached.
The 3-angled seeds may be smooth or hairy.