- Deadnettles and Mints
yellow archangel or yellow deadnettle, Lamium
(Queendown Warren Nature Reserve, Kent, UK).
and below: Bugle, Ajuga
(Cromer's Wood, Kent, UK). Often
the square stem is only hairy on two opposite sides. Floral
C(5) A4 G(2). All photos on this
page can be enlarged by clicking on them.
white archangel or white deadnettle, Lamium
(click image to enlarge). Below: a common feature
lamiates, including both Lamium
is the arrangement of flowers in tiers of about six or
more. However, in the deadnettle there are clearly only two
leaf-like bracts per tier of flowers, so we have two
main branches off the central axis at each node. These bracts are
sometimes considered leaves, they are
primary bracts subtending an inflorescence, rather than secondary
bracts (bracteoles) subtending an individual
flower. The bracteoles are visible as the small green spikey
leaflike structure beneath each flower unit. What we
have are sympodial
off a monopodial
in which the branches each bear several flowers. (See
The axis is really the vegetative axis and each branch is an
inflorescence, though together the
tiers of flower-bearing branches and central axis create a
composite inflorescence which is a flower spike. Each
inflorescence branch is a type of inflorescence called a cyme,
meaning it is sympodial and, initially at least, it is
meaning that each unit (node + internode) of the cyme produces two
flowers. However, the
picture may be further complicated in some plants of this type as
each unit may secondarily become
monochasial, bearing only one flower per unit. The resulting
'whorl' of flowers making up a tier is therefore
actually a false whorl called a verticillaster.
thrives in damp woods, meadows and pastures. Here a large number
were found amongst
primroses (Primula) and early purple
is perennial, growing to 10 to 30 cm in height from a short
rhizome (underground stem). The inflorescence grows
from a basal rosette of leaves. The square stems are often hairy
on two opposite sides only (in this case they
were more-or-less hairy on all four sides). These plants can
reproduce asexually by means of long, leafy, rooting
stolons. Typical of lamiates the flowers have bilateral
The flowers are hermaphroditic, appear in
early spring and are blue (rarely pink or white) and usually
appear in 6-flowered whorls in the axils of the leaf-like
bracts visible in the photo above. Protandry is common in lamiates.
In protandry the male organs ripen first and
the female organs ripen later, so that the flower, although
hermaphroditic, is functionally male first, female later -
a mechanism which reduces or prevents inbreeding. The stamens
ripen first, whilst the stigma is held well above,
out of the way of pollinating insects, and later bends down to
near the entrance to the corolla ( which forms a
petal tube) so as to receive pollen. There is a nectary at the
base of the ovary and bees and other insects
pollinate these flowers.
The lamiaceae (labiatae) consists of plants such as the
deadnettles and mints, which are called lamiates or
verticillaster of false-whorl (pseudowhorl) of flowers in Lamium
This whorl actually consists of two very short sympodial branches.
white deadnettle is also protandrous - in the initial male stage
the stigma is held well away from the
flower opening and out of the way of visiting insects. Later on
the flower becomes functionally female,
and the stigma is brought near the entrance to receive pollen from
visiting insects. The half-flowers,
floral diagram and floral formula of Lamium
are shown below.
that although most parts of the flower occur in groups of five,
there are only four stamens. The missing stamen is sometimes
represented as a dot in floral diagrams (not shown here).
the red deadnettle, Lamium
is often a much smaller plant than Lamium
with smaller flowers. (Left:
Cromer's Wood, Kent, UK; right: Milton Creek, Kent, UK) but can
reach 30 cm (12 inches) in height. Below: a tall specimen from
Bredhurst (Kent, UK).
ground ivy (Glechoma
is another labiate. (Borden
Nature Reserve, Kent, UK).
Below: Queendown Warren (Kent, UK).
5th Oct 2014
16th March 2015
25 May 2015
4 July 2015
24 June 2017
7 May 2018
25 June 2019
Above: Hedge Woundwort (Stachys sylvatica).
nigra (Black Horehound) - a microscopical study
(Black Horehound) emits a
distinctive harsh musky or resinous odour when
damaged. It is a perennial herb and often a tall
plant, up to 80 cm in height. It is commonly
found on hedge-banks and roadsides. It is
described as hairy and under the microscope
the hairs on the floral parts are vividly apparent.
The upper lip is slightly concave and the lower
lip divided into small lateral lobes and a large
central lobe. The flowers are borne on the leaf
of the sepal funnel (calyx) is lined by
glandular hairs. If you click on these
thumbnails to enlarge them, then you will see
capitate hairs (hairs ending in spherical heads
like tiny pins) around the rim of the calyx. This
morphology is typical of secretory hairs. Often
the function of such glandular hairs is
uncertain or completely unknown. They are
common on the aerial parts of Lamiaceae and
their distribution is of taxonomic significance.
Along with a second type of secretory hair
often found (peltate hairs) the capitate hairs
secrete the specific essential oil characteristic
is secreted beneath the thin covering cuticle which swells like a
balloon before eventually rupturing to release the volatile
oil. The essential oil of Black Horehound has been shown to have
antimicrobial powers. Perhaps these glandular hairs are
positioned to protect the nectar from ants crawling up the stem.
Ants reportedly often steal nectar from plants, often without
efficiently pollinating flowers intended for other types of
the flowers in detail, protandry is evident. In
the flower with freshly opened anthers (x 4) still packed
with white pollen, on the left, the stigma is not readily
visible. However, in the flower on the right which has
lost most of its pollen (presumably the anthers have
been dehisced for longer) the bifid (forked) stigma is
readily visible bending forwards (downwards when on
the plant) into position to intercept pollen from visiting
insects. In the top right is a flower with one anther in
prime position to intercept a visiting insect.
upper (adaxial) surface of a young leaf of
Right: the undersurface (abaxial
surface) of the same leaf, showing hairs along the
veins. This is a common feature in many plants and
possibly protects the phloem from sap-feeding
a square stem?
characteristic of lamiates (and some other herbaceous plants) is
that the stem is distinctly squarish in cross-section. The main
vascular bundles are situated near the four corners (smaller
bundles are often situated midway between each pair of corners).
four corners contain ridges rich in collenchyma - cells with
heavily thickened cellulose cell walls. This arrangement optimises
mechanical strength, whilst being more resource effective than
forming a complete cylinder of collenchyma. Having the vascular
bundles situated towards the periphery makes the stem stiffer (the
moment of bending is increased), since xylem is a strong tissue.
The four longitudinal ridges of collenchyma also add strength.
Collenchyma forms slightly elastic but tough tissues to help the
resist bending forces. Collenchyma is also plastic and will flow
and deform to accommodate growth of the stem.
yellow archangel, Lamiastrum
has an interesting biology. Most forms can reproduce asexually
by means of stolons or suckers (a horizontal shoot which roots at
intervals to produce new plants) which run either
beneath the ground or along it and which may bear leaves. Three
main subspecies are naturally occurring in
Europe: subspecies montanum,
and flavidum. In Britain only montanum and galeobdolon occur
naturally, flavidum (which unlike the others
does not form stolons) occurs in mountainous regions on
Europe, such as the Central and Eastern Alps. In the 1980s another
escaped from horticulture and became naturalised and is now the
most widespread in Britain and
Ireland, occurring in most regions. Montanum is quite widespread in
england and Wales but very scattered in
Scotland. It grows in woodlands and hedges, apparently preferring
woodland edges to deeply shaded areas and
occurs in beechwoods on limestone, and in oak-ash woods along with
anemones, arums, primulas, Ajuga
(Bugle), Dog's Mercury and Wood Sanicle.
Subspecies argentatum, also known as
variegated yellow archangel, has 'variegated leaves' which
colourless regions which contain air pockets (these are much less
frequent in the other subspecies). This invasive
form was bred from native European forms. Telling subspecies montanum and galeobdolon apart is not so easy.
Subspecies galeobdolon is diploid (it has two
copies, 2n, of n chromosomes) with 18 chromosomes (n = 9)
whereas montanum is tetraploid (4n) with
36 chromosomes. Montanum is more vigorous and is
generally a taller
plant at 20-60 cm compared to 15-45 cm for galeobdolon and more flowers per
whorl (more than 8 compared with
less than 8) and more whorls per inflorescence (4-7, sometimes
3-10, compared with 2-4, sometimes 5). The
upper bracts and stolon leaves of subspecies galeobdolon tend to have more
crenate (rounded) teeth whereas
the teeth tend to be more serrate (pointed) in montanum. However, all these
characteristics overlap, a montanum
growing in poorer conditions may resemble galeobdolon in vigour. However, a
study by Wegmuller (Wegmuller, S,
1971. A cytotaxonomic study of Lamiastrum
(L.) Ehrend. & Polatschek in Britain. Watsonia, 8:
277-288) showed a good separation of the two if one considers
stomatal length together with bract length to width
ratio (l/w): ssp. galeobdolon has a bract l/w of about
0.9 to 1.8 and a stomatal length of 24 to 28 micrometres;
montanum has a bract l/w of 1.4
to 4 and a stomatal length of 28 to 36 micrometres.
It has been suggested that ssp. montanum is a hybrid of ssp. galeobdolon and ssp. flavidum as its characteristics
are intermediate. This would make it an allotetraploid - a tetraploid with two
chromosome sets from one species
(or subspecies) and two from another.
Ssp. argentatum was favoured by
gardeners partly because it easily spreads forms dense leaf
cover. Although it
does not set seed it reproduces rapidly by stolon formation. this
characteristic makes it a potential threat as an
invasive alien species, a potential problem being investigated by
prof. Ian rotherham of Sheffield hallam University,
views of the flower of
anthers and two stigmas are
The flower is, like Lamium
pollinated by bees and in both
species a significant quantity of
nectar can often be found in the
base of the flower.Studies in L.
have shown that sticky
trichomes on the anther, near the
dehiscence slit from which pollen is
released, trap some of the pollen
grains. Observations suggest
these act as pollen
presenting pollen as a food reward
to visiting insects (sacrificing some
pollen so that other pollen has a
chance of successful pollination).
and right: a cross-section of the stem of
Lamium through an internode.
The cortex and
medulla (pith) are composed of parenchyma
cells; smaller cells are found in the outer than in
the inner cortex and the largest parenchyma cells
occupy the medulla. The central pith has broken
down to form a central pith cavity, as it failed to
keep up with rapid stem elongation. In this type of
stem, central pith typically remains in the nodes,
forming nodal diaphragms. Collenchyma with
massively thickened walls occurs in the
longitudinal ridges or angles of the stem.
Collenchyma with thinner walls also occurs in the
vascular bundles, forming the vascular sheath.
The vascular cambium, consisting of several
layers of mitotically active parenchyma cells,
forms secondary xylem and phloem. In some
lamiates, the interfascicular cambium (layers of
parenchyma in between vascular bundles which
is continuous with the vascular cambium)
produces sclerenchyma as the stem matures.
petals and stamens of L.
are thought to secrete scent (epidermal glands on the filament and
trichomes on the anther are thought to secrete this, along with
secretory trichomes and papillae on the petals, though
establishing the function of individual secretions is not easy).
The nectary of L.
consists of four lobes surrounding the
base of the ovary. 'Teeth' on the sides of the lower lip in Lamium album have been shown to
support the legs of visiting insects
and the lateral teeth seen here in Lamium
possibly perform the same function. (See: Sulborska, A., M.
Konarska, and E. Weryszko-Chmielewska, 2014. Adaptations of Lamium album L. flowers to
pollination by Apoidea. Acta
Pol., Hortorum Cultus
and left: Salvia
(Meadow Clary or Meadow
Sage) (Queendown Warren, Kent, Britain). This plant is
threatened in Britain.
The curious viper-like flowers employ a staminal-lever
(see the half-flower diagram below).
The two anthers lie side-by-side and both have the same form:
a short filament forks into a connective which joins the two
anther lobes. The topmost anther lobe is fertile and produces
pollen (it is unilocular) whereas the lower lobe is sterile. The
connective pivots on a hinge with the filament. Together the
two sterile lobes form a shield.
When a pollinating insect, visiting a young flower, forces its way
to the nectar at the base of the floral tube (corolla) it pushes
the shield forwards, causing the connective to pivot, swinging
the fertile lobe downwards to dab pollen on the insect's back.
Older flowers enter a female stage, in which the style has been
brought down into position to receive pollen from the back of a
diagrams for use in
and below: Selfheal, Prunella
This plant was used as a cure-all in Medieval times. Science has
since shown that the Lamiaceae have a wide variety of medicinal
uses and Selfheal is no exception. Aqueous extracts of this plant
have been shown to greatly inhibit the ability of HIV-1
(the most aggressive strain of Human Immunodeficiency Virus which
causes AIDS) to infect cells in culture. (See: Oh et al.,
8:188 Inhibition of HIV-1 infection by aqueous extracts of Prunella vulgaris L.).
Above: a white variety of Selfheal. This plant is lacking
anthocyanin pigment in the petals and sepals. Prunella vulgaris
occurs in a number of beautiful forms, such as these forms from
Close up view of the flowers (click image for full size).
Above: Stachys sylvatica - unfurling flowers up close.
the uncommon white variety of Bugle. In some plants white forms
due to genetic mutation blocking synthesis of anthocyanin pigments
plants their red, purple and blue colours.
yellow archangel or yellow deadnettle, Lamium
Above: Wild Marjoram, Origanum vulgare, growing on
calcareous soil. Habitat: grasslands, scrub, hedgebanks, on
calcareous soils. Note the characteristic protruding stamens.