Hellebore Structure
Acaulescent Hellebores
The term acaulescent means "without a stem" and applies to the vast majority of
hellebore plants traditionally grown in gardens. Leaves and flower stalks emerge
separately from the rhizome growing underground, and there is (usually) no
apparent stem-like protrusion. Anomalies can be found, however, so the term is
used here pragmatically.
The rhizome in acaulescent plants is thick and well developed, usually clearly
distinguishable from the aerial parts. Rhizomes are branched in mature plants to
varying degrees. These structures are sympodial, i.e. new growth occurs at the
base of last season's growth. Old roots are thick and fleshy, often brown to black.
Further toward the root tips, new growth develops on branched rootlets that may
appear white to black. The portion of the roots furthest away from the rhizome are
the most active; they are also the most fragile and can easily break when
disturbed.
In many acaulescent plants, leaves are clearly pedate but some appear palmate
(e.g. Helleborus purpurascens), and in other cases leaves are weakly pedate or
palmate, often somewhere in between. Leaves are divided into leaflets which can
be further divided into many divisions, from part to nearly all their length. The
petiole rises directly from the ground level at the base of the previous season's
growth, often but not always after the inflorescence which is produced on a
leafless scape-like flower stalk. Foliage is large and substantial with
conspicuous veining on the undersides. Plants may be glabrous or pubescent or
anything in between. Often hairs are most noticeable along the vein margins.
Helleborus orientalis and its hybrids often have overwintering leathery leaves
which persist for up to one year. Other acaulescent species and hybrids typically
have leaves that are autumn and winter dormant. In Helleborus thibetanus, leaves
may enter dormancy during summer. Dormancy is broken in late winter or early
spring. in Helleborus bocconei and Helleborus liguricus, leaves may break
dormancy in late autumn and continue to grow throughout the winter months,
particularly in mild winter climates.
In acaulescent plants the inflorescence arises directly from ground level at the
base of the last season's growth on the rhizome, often but not always before the
appearance of true leaves. The flower stalk bears no true leaves but leaf-like
bracts are common; consequently, inflorescences may have a bushy appearance.
The flower structure of hellebores is somewhat different than that of most other
garden plants. Petals typically provide flower color and are often protected by a
calyx in most garden plants. In hellebores, no calyx in this sense is present, and
the only thing resembling petals comes in the form of tubular nectaries at the
base of the sepals. These nectaries provide food for pollinators, though many
pollinators are likely attracted by ultraviolet reflections by the much larger sepals.
Nectaries last but a short time and are shed along with the stamens by the time
carpels begin to swell with fertilized ovules.
Sepals provide the flower color and main horticultural attraction in hellebore
flowers, but they function differently than do petals and are much more responsive
to environmental factors. Most noticeably, the sepals remain on the flower long
after fertilization and never really fall off. They simply change colors and eventually
dessicate and deteriorate along with the entire inflorescence. The sepals most
commonly number five and consist of two outer sepals, two inner sepals, and one
that has an edge inside and outside the edges of adjacent sepals. The outer two
sepals provide some protection from the elements and are often a different color
than the innermost sepals, particularly after prolonged exposure to sunlight, cold,
wind, and precipitation.
Sepals undergo a significant amount of photosynthetic activity compared to
petals. After fertilization, photosynthetic activity usually increases in hellebore
plants so that in the fruiting stage the sepals turn greener or darker green.
Citokinins and gibberellins activate chloroplasts after fertilization, and this activity
is later slowed in the fruiting phase. Throughout this photosynthetic process the
peduncles and petioles elongate and sepals broaden and spread apart, which is
believed to aid in the distribution of seed. In some plants the sepals do not turn
green after fertilization, and this is most obvious in dark flowers that possess
permanent anthocyanins.
The interior of the perianth consists of a cluster of stamens tightly surrounding the
carpels, which in turn surrounds the pistils. Generally, the pistils are receptive to
pollen before the stamens mature, which is useful for cross-pollination and is a
fortunate aspect of hellebore morphology from a breeding/hybridizing perspective.
As the stamens elongate the anthers begin to produce pollen. The anthers then
often curve outward away from the gynoecium. Flowers are hermaphroditic and
generally self-fertile, and thus do not need other plants nearby to reproduce.
Comments on individual flower photos:
1. Notice that the two greenish sepals are the two outermost ones. Also, the one
that has one outer edge also shows this greening. The two interior sepals are
mostly unspoiled. This characteristic is most noticeable on the first flowers of the
year. Those that open in more favorable weather a bit later on often remain
unaffected or only slightly so.
2. Notice that there is no real calyx here and that the sepals connect directly to the
end of the pedicel. Since many hellebore flowers nod, the color on the outside of
the sepals can be important for horticultural interest.
3. Example showing photosynthesis in older sepals. The white one on the left
opened later.
4. In most hellebore flowers the sepals turn greenish or greener after fertilization
regardless of the original color. In some, however, the color is preserved. Here
the anthocyanins remain active and give the perianth a dark appearance even in
the fruiting stage. The capsules are also dark, providing an interesting aesthetic
effect.
5. The interior of this flower shows signs of doubling at the nectary level. The
necaries are no longer functioning and here this region has taken on the
appearance and color of small sepals.
6. The most common double form where the interior develops rows of sepal-like
material but the outer sepals are 'normal'.
7. Here the stamens are still tightly wound around the gynoecium, and the anthers
have yet to produce mature pollen. At this stage the pistils are almost certainly
receptive to pollen and probably have been for some time.
8. Here stamens are beginning to elongate and slowly turn away from the
gynoecium. Anthers will soon be producing copious amounts of pollen.
Caulescent Hellebores
Caulescence is defined by the presence of a prominent above-ground stem. For
practical purposes, this term can aptly be used to describe Helleborus foetidus,
Helleborus lividus, and Helleborus argutifolius. These three hellebore species
have much-reduced root systems and a central stem that exhibits strong upward
growth, bearing the leaves and flowers. Here we will focus mostly on the general
idealized properties. For information on each species, please refer to the species
pages.
The rhizome of caulescent hellebores is largely unbranched and simple. Roots
extend downward from one end, and vegetative growth emerges from the other
end toward the surface. This makes caulescent hellebores impractical to
reproduce through division. Their root masses are remarkably small relative to
other plants in the genus; yet, interestingly, caulescent hellebores seem no less
drought tolerant than most deep-rooted acaulescent plants, and are more drought
tolerant than some. Their small root system and large vegetative mass make
them challenging to transplant or move into pots once they approach or reach
maturity. These same morphological features make them top heavy, and
sometimes stems will bend under the weight of the foliage and inflorescences.
As the aerial stems elongate and mature, the lower parts of the stems harden
and become semi-woody. Leaves develop in a similar manner to other dicots in
that the petiole elongates and the leaf base thickens, each becoming determinate
before the flowering shoot meristem. Healthy petioles generally grow upward at
acute angles, but the leaves may descend as a result of wind, ice or snow, and
gravity.
Acaulescent Hellebores
The term acaulescent means "without a stem" and applies to the vast majority of
hellebore plants traditionally grown in gardens. Leaves and flower stalks emerge
separately from the rhizome growing underground, and there is (usually) no
apparent stem-like protrusion. Anomalies can be found, however, so the term is
used here pragmatically.
The rhizome in acaulescent plants is thick and well developed, usually clearly
distinguishable from the aerial parts. Rhizomes are branched in mature plants to
varying degrees. These structures are sympodial, i.e. new growth occurs at the
base of last season's growth. Old roots are thick and fleshy, often brown to black.
Further toward the root tips, new growth develops on branched rootlets that may
appear white to black. The portion of the roots furthest away from the rhizome are
the most active; they are also the most fragile and can easily break when
disturbed.
In many acaulescent plants, leaves are clearly pedate but some appear palmate
(e.g. Helleborus purpurascens), and in other cases leaves are weakly pedate or
palmate, often somewhere in between. Leaves are divided into leaflets which can
be further divided into many divisions, from part to nearly all their length. The
petiole rises directly from the ground level at the base of the previous season's
growth, often but not always after the inflorescence which is produced on a
leafless scape-like flower stalk. Foliage is large and substantial with
conspicuous veining on the undersides. Plants may be glabrous or pubescent or
anything in between. Often hairs are most noticeable along the vein margins.
Helleborus orientalis and its hybrids often have overwintering leathery leaves
which persist for up to one year. Other acaulescent species and hybrids typically
have leaves that are autumn and winter dormant. In Helleborus thibetanus, leaves
may enter dormancy during summer. Dormancy is broken in late winter or early
spring. in Helleborus bocconei and Helleborus liguricus, leaves may break
dormancy in late autumn and continue to grow throughout the winter months,
particularly in mild winter climates.
In acaulescent plants the inflorescence arises directly from ground level at the
base of the last season's growth on the rhizome, often but not always before the
appearance of true leaves. The flower stalk bears no true leaves but leaf-like
bracts are common; consequently, inflorescences may have a bushy appearance.
The flower structure of hellebores is somewhat different than that of most other
garden plants. Petals typically provide flower color and are often protected by a
calyx in most garden plants. In hellebores, no calyx in this sense is present, and
the only thing resembling petals comes in the form of tubular nectaries at the
base of the sepals. These nectaries provide food for pollinators, though many
pollinators are likely attracted by ultraviolet reflections by the much larger sepals.
Nectaries last but a short time and are shed along with the stamens by the time
carpels begin to swell with fertilized ovules.
Sepals provide the flower color and main horticultural attraction in hellebore
flowers, but they function differently than do petals and are much more responsive
to environmental factors. Most noticeably, the sepals remain on the flower long
after fertilization and never really fall off. They simply change colors and eventually
dessicate and deteriorate along with the entire inflorescence. The sepals most
commonly number five and consist of two outer sepals, two inner sepals, and one
that has an edge inside and outside the edges of adjacent sepals. The outer two
sepals provide some protection from the elements and are often a different color
than the innermost sepals, particularly after prolonged exposure to sunlight, cold,
wind, and precipitation.
Sepals undergo a significant amount of photosynthetic activity compared to
petals. After fertilization, photosynthetic activity usually increases in hellebore
plants so that in the fruiting stage the sepals turn greener or darker green.
Citokinins and gibberellins activate chloroplasts after fertilization, and this activity
is later slowed in the fruiting phase. Throughout this photosynthetic process the
peduncles and petioles elongate and sepals broaden and spread apart, which is
believed to aid in the distribution of seed. In some plants the sepals do not turn
green after fertilization, and this is most obvious in dark flowers that possess
permanent anthocyanins.
The interior of the perianth consists of a cluster of stamens tightly surrounding the
carpels, which in turn surrounds the pistils. Generally, the pistils are receptive to
pollen before the stamens mature, which is useful for cross-pollination and is a
fortunate aspect of hellebore morphology from a breeding/hybridizing perspective.
As the stamens elongate the anthers begin to produce pollen. The anthers then
often curve outward away from the gynoecium. Flowers are hermaphroditic and
generally self-fertile, and thus do not need other plants nearby to reproduce.
Comments on individual flower photos:
1. Notice that the two greenish sepals are the two outermost ones. Also, the one
that has one outer edge also shows this greening. The two interior sepals are
mostly unspoiled. This characteristic is most noticeable on the first flowers of the
year. Those that open in more favorable weather a bit later on often remain
unaffected or only slightly so.
2. Notice that there is no real calyx here and that the sepals connect directly to the
end of the pedicel. Since many hellebore flowers nod, the color on the outside of
the sepals can be important for horticultural interest.
3. Example showing photosynthesis in older sepals. The white one on the left
opened later.
4. In most hellebore flowers the sepals turn greenish or greener after fertilization
regardless of the original color. In some, however, the color is preserved. Here
the anthocyanins remain active and give the perianth a dark appearance even in
the fruiting stage. The capsules are also dark, providing an interesting aesthetic
effect.
5. The interior of this flower shows signs of doubling at the nectary level. The
necaries are no longer functioning and here this region has taken on the
appearance and color of small sepals.
6. The most common double form where the interior develops rows of sepal-like
material but the outer sepals are 'normal'.
7. Here the stamens are still tightly wound around the gynoecium, and the anthers
have yet to produce mature pollen. At this stage the pistils are almost certainly
receptive to pollen and probably have been for some time.
8. Here stamens are beginning to elongate and slowly turn away from the
gynoecium. Anthers will soon be producing copious amounts of pollen.
Caulescent Hellebores
Caulescence is defined by the presence of a prominent above-ground stem. For
practical purposes, this term can aptly be used to describe Helleborus foetidus,
Helleborus lividus, and Helleborus argutifolius. These three hellebore species
have much-reduced root systems and a central stem that exhibits strong upward
growth, bearing the leaves and flowers. Here we will focus mostly on the general
idealized properties. For information on each species, please refer to the species
pages.
The rhizome of caulescent hellebores is largely unbranched and simple. Roots
extend downward from one end, and vegetative growth emerges from the other
end toward the surface. This makes caulescent hellebores impractical to
reproduce through division. Their root masses are remarkably small relative to
other plants in the genus; yet, interestingly, caulescent hellebores seem no less
drought tolerant than most deep-rooted acaulescent plants, and are more drought
tolerant than some. Their small root system and large vegetative mass make
them challenging to transplant or move into pots once they approach or reach
maturity. These same morphological features make them top heavy, and
sometimes stems will bend under the weight of the foliage and inflorescences.
As the aerial stems elongate and mature, the lower parts of the stems harden
and become semi-woody. Leaves develop in a similar manner to other dicots in
that the petiole elongates and the leaf base thickens, each becoming determinate
before the flowering shoot meristem. Healthy petioles generally grow upward at
acute angles, but the leaves may descend as a result of wind, ice or snow, and
gravity.
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Many flying insects
benefit from the flowers
of hellebores. True bees
and the occasional wasp
serve as the main
facilitators of pollination
in my garden, but in the
last photo, which was
taken at a native site in
Croatia, hairy beetles
could be seen (often
caked in pollen) flying
from plant to plant.
benefit from the flowers
of hellebores. True bees
and the occasional wasp
serve as the main
facilitators of pollination
in my garden, but in the
last photo, which was
taken at a native site in
Croatia, hairy beetles
could be seen (often
caked in pollen) flying
from plant to plant.