Plantain Family - Plantaginacea
|Water Plantain Family - Alismataceae
Great Plantain (Plantago major).
Ribwort (Plantago lanceolata) has narrower (lanceolate)
leaves than Plantago major and shorter flower spikes.
The flower spikes are also a darker colour. Although
thought to be wind-pollinated it has recently been
observed that honeybees frequent the flowers.
The tall inflorescence springs from a rosette of leaves and bears many flowers clustered together in a spike.
The flowers develop first at the base of the spike and the female parts mature before the male parts
(protogyny). The whorl of white hairlike tufts seen protruding in the specimen above are the anthers of the
mature male flowers. This separation in time, between the development of the female and male organs helps
promote cross-pollination. Even though plantains may exhibit genetic self-incompatibility (meaning that its
own pollen grains will not germinate when in contact with the female stigmas of the same plant, protogyny
reduces pollen-pistil interference which occurs when the plant's own (incompatible) pollen clogs the stigmas,
reducing the likelihood that pollen from another plant will attach. (The pistil is the female part of the flower,
comprising one or more carpels that may be fused together). Plantains are wind-pollinated monocotyledons.
Above, the water plantain, Alisma plantago-aquatica, were so-named because of the
resemblance of their leaves to those of Plantago, but actually belongs to a totally different family
of monocots. It grows in mud by ponds and slow-moving rivers. The flowers are borne on
pyramidal inflorescences, each at the end of a long stalk and each flower is up to 1 cm across
and has three lilac to white petals. Another species occurs in the same habitat: Alisma
lanceolatum, which has narrower (more lanceolate) leaves with less rounded, more tapered
(cuneate) leaf bases. However, leaf shape is highly variable and overlaps between the two
species, such that the only reliable form of classification is to look at the carpels or fruit
(achenes). In Alisma plantago-aquatica the single style is at the top of the ovary, but off to one
side. It maintains this lateral position as the ovary expands and develops into the achene. In
Alisma lanceolatum, the style begins at the apex of the ovary, in a much more central position.
However, as the achene develops it swells over and the top over-arches the style which gets
displaced more laterally. In mature A. lanceolatum the style may be anchored slightly more
towards the apex of the achene, but there is considerable variation. For definite identification the
young carpels have to be examined, with several being examined from each plant.
Above and below: achenes from Alisma plantago-aquatica, showing the remains of the style
attached laterally. Mature achenes of Alisma lanceolatum may be similar, though there is a
tendency for the style to be slightly more towards the top (more apical) though this depends on
maturity. In Alisma plantago-aquatica a more distinctive keel may reveal the more lateral original
position of the style in the achene.
Above: the differences in the developing carpels becomes readily apparent. A: Alisma
plantago-aquatica, immature carpel; B: Alisma plantago-aquatica, carpel beginning to
develop; C: Alisma lanceolatum, immature carpel.
To further complicate taxonomy a hybrid form between A. plantago-aquatica and A.
lanceolatum, called Alisma x rhicnocarpum. The leaf shape is intermediate in these
forms and so more like a rectangle with rounded corners in contour. However, this is
perhaps more easily identified by the fact that it is almost entirely sterile with only one or
two achenes developing in each flower (are these sterile?). It will thus usually be found
in the vicinity of both parents.
Note the lateral positions of the style remains.