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Hellebore

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Hellebore
19th century illustration of Helleborus niger
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Order: Ranunculales
Family: Ranunculaceae
Subfamily: Ranunculoideae
Tribe: Helleboreae
Genus: Helleborus
L.[1]
Species

See text.

Commonly known as hellebores (/ˈhɛlɪbɔːrz/), the Eurasian[2] genus Helleborus consists of approximately 20 species of herbaceous or evergreen perennial flowering plants in the family Ranunculaceae, within which it gave its name to the tribe of Helleboreae. Despite names such as "winter rose",[3] "Christmas rose" and "Lenten rose", hellebores are not closely related to the rose family (Rosaceae).[4] Many hellebore species are poisonous.

Taxonomy

The genus was established by Carl Linnaeus in volume one of his Species Plantarum in 1753.[1]

The scientific name Helleborus derives from the ancient greek word ἑλλέβορος (helléboros), the name for H. orientalis, constructed from ἑλεῖν (heleîn), meaning "to injure", and βορά (borá), meaning "food".[5][6][7]

Distribution and description

Helleborus thibetanus
Seed pods swell
Helleborus odorus (at NYBG)
Hellebore species and hybrids: Helleborus viridis (top left); H. foetidus (top right) with cross-section; flowers of various specimens of H. × hybridus, including doubles

Various species of this genus originated in Europe and Asia.[8] The greatest concentration of species occurs in the Balkans. One atypical species (H. thibetanus) comes from western China; another atypical species (H. vesicarius) inhabits a small area on the border between Turkey and Syria.

The flowers have five petal-like sepals surrounding a ring of small, cup-like nectaries which are actually "petals" modified to hold nectar. The sepals do not fall as petals would, but remain on the plant, sometimes for many months. Recent research in Spain suggests that the persistence of the sepals contributes to the development of the seeds (Herrera 2005).

Distribution maps of 19 species of Helleborus in Europe und Asia (top) and in southeast europe (bottom). (Try according the natural distribution)

Horticulture

Hellebores are widely grown in USDA Zone 5a to 8b gardens for decorative purposes. They are particularly valued by gardeners for their winter and early spring flowering period; the plants are surprisingly frost-resistant and many are evergreen.[9] Also of value is their shade tolerance.[3] Many species of hellebore have green or greenish-purple flowers and are of limited garden value, although Corsican hellebore (H. argutifolius), a robust plant with pale green, cup-shaped flowers and attractive leathery foliage, is widely grown. So is the 'stinking hellebore' or setterwort (H. foetidus), which has drooping clusters of small, pale green, bell-shaped flowers, often edged with maroon, which contrasts with its dark evergreen foliage. H. foetidus 'Wester Flisk', with red-flushed flowers and flower stalks, is becoming popular, as are more recent selections with golden-yellow foliage.

The so-called Christmas rose (H. niger), a traditional cottage garden favourite, bears its pure white flowers (which often age to pink) in the depths of winter; large-flowered cultivars are available, as are pink-flowered and double-flowered selections.

The most popular hellebores for garden use are H. orientalis and its colourful hybrids, H. × hybridus (Lenten rose).. In the northern hemisphere, they flower in early spring, around the period of Lent, and are often known as Lenten hellebores, oriental hellebores, or Lenten roses. They are excellent for bringing early colour to shady herbaceous borders and areas between deciduous shrubs and under trees.

The cultivar Walberton's Rosemary='Walhero' (sometimes listed under H. × hybridus) has won the Royal Horticultural Society's Award of Garden Merit.[10]

Species and subspecies

Twenty two species are recognised and divided into six sections.[11] The table below shows the species of the genus helleborus, give its common name, the area of distribution, an image if available and the meaning of the scientific name. [11], [12], [13] The cladogram shows the relationship between the different species determined with microbiological methods by Meiners et al. (2011) .[11]

Name Common name meaning of the scientific name Distribution area Color of the flower Image
Subgenus Helleborus
I. sect. Griphopus Spach em. Schiffner foot of a gryphon
Helleborus foetidus L.
1753		 stinking hellebore or setterwort stinking SW – M Europe green, commonly red rim
II. sect. Chenopus Schiffner meandering
Helleborus lividus Aiton
1789		 lead colored, bluish Majorca green
Helleborus argutifolius Viv.
1824		 often H. lividus Aiton ssp. corsicus (BRIQ.) P. FOURN. many leafs Corsica, Sardinia green, white
III. sect. Helleborus
[sect. Chionorhodon Spach]		 snow, rose
Helleborus niger L.
1753		 Christmas rose or black hellebore black Croatia, Slovenia, N Italy, Switzerland, Austria, S Germany white, later pink
subsp. macranthus white, later pink
subsp. niger L. white, later pink
Subgenus Helleborastrum (Spach)
IV. sect. Syncarpus Schiffer similar to a carpus
Helleborus vesicarius
Aucher ex Boiss. 1841		 SE Turkey, NW Syria red
V. sect. Dicarpon Ulbrich not like a carpus
Helleborus thibetanus Franch.
1885		 China pink
VI. sect. Helleborastrum Spach similar to hellebore
Helleborus abruzzicus
M.Thomsen, McLewin & B.Mathew 		Abruzzo middle Italy whitish, greenish
Helleborus atrorubens
Waldst. & Kit. 1812		 dark, red Slovenia, N Croatia, Bosnia,
former Yugoslavia		 reddish, purple
Helleborus bocconei
Ten. 1823		 Botanist Paolo Boccone S Italy, Sicily white
Helleborus croaticus
Martinis 1973		 from Croatia NE Croatia reddish violet
Helleborus cyclophyllus
(A.Braun) Boiss. 1867		 Circle, leafs Greece, Macedonia, Albania, Bulgaria green, light green, whitish
Helleborus dumetorum
Waldst. & Kit. ex Willd. 1809		 Slovenia, Hungary, Croatia, Romania, Austria, green to white
Helleborus liguricus
M.Thomsen, McLewin & B.Mathew		 from Liguria Italy (Ligura, Tuscany) green to white
Helleborus multifidus
Vis. 		multiple segmented Croatia, Herzegovina green
subsp. hercegovinus from Herzegovina Montenegro, Hercegovina yellow-green
subsp. istriacus from Istria NE Italy, Croatia, Bosnia, Montenegro green
subsp. multifidus multiple segmented Albania and former Yugoslavia
Helleborus odorus
Waldst. & Kit. ex Willd. 1809		 odorant S- and SE Europe with
focus at the Balkans		 green bis yellowish-green
subsp. odorus L. odorant
Helleborus orientalis Lam.
1789		 Lenten rose, Lenten hellebore, oriental hellebore from the east N Turkey, Bulgaria, Ukraine, Georgia, Caucasus white, yellowish, pink
subsp. abchasicus
(A. Braun) Mathew		 from Abchasia Georgia pink, reddish
subsp. guttatus
(A. Braun & Sauer) Mathew		 dotted
subsp. orientalis H. caucasicus, H. kochii from the east occasionally used for ssp. gutatus + abchasicus reddish
Helleborus purpurascens
Waldst. & Kit. 1802		 purple / red Hungary, Slovakia, Poland, Romania violet, brown
Helleborus torquatus
Archer-Hind 1884		 adorned with a necklet Croatia, Bosnia, Serbia, Montenegro green, violet
Helleborus viridis L.
1753		 green hellebore or bear's-foot green Austria, N Italy, Swizerland, S Germany green
subsp. occidentalis
1869		 from the west N Spain, SW France (France, Germany, Great Britain naturalised) green
 Subgenus Helleborus
 sec. Griphopus 

H. foetidus

 sec. Helleborus 

H. niger

 sec. Chenopus 

H. argutifolius

H. lividus

   
 Subgenus Helleborastrum
  sec. Syncarpus 

H. vesicarius

  sec. Dicarpon 

H. thibetanus

  sec. helleboastrum 

H. dumetorum

H. purpurascens

H. croaticus

H. multifidus

H. abruzzicus    

H. hercegovinus

H. liguricus      

H. atrorubens

H. viridis    

H. cyclophyllus

H. torquatus      

H. orientalis           

H. odorus

Cladogram of evolutionary lines in Helleborus from Meiners et al.(2011) [11]

Caulescent species

These four species have leaves on their flowering stems (in H. vesicarius the stems die back each year; it also has basal leaves).

Acaulescent (stemless) species

These species have basal leaves. They have no true leaves on their flower stalks (although there are leafy bracts where the flower stalks branch).

Other species names (now considered invalid) may be encountered in older literature, including H. hyemalis, H. polychromus, H. ranunculinus, H. trifolius.

Hellebore hybrids

H. × hybridus in a garden

Hybridising (deliberate and accidental) between H. orientalis and several other closely related species and subspecies has vastly improved the colour-range of the flowers, which now extends from slate grey, near-black, deep purple and plum, through rich red and pinks to yellow, white and green. The outer surface of the sepals is often green-tinged, and as the flower ages it usually becomes greener inside and out; individual flowers often remain on the plant for a month or more. The inner surface of each sepal may be marked with veins, or dotted or blotched with pink, red or purple. "Picotee" flowers, whose pale-coloured sepals have narrow margins of a darker colour, are much sought-after, as are those with dark nectaries which contrast with the outer sepals.

Recent breeding programmes have also created double-flowered and anemone-centred plants. Ironically, doing this is actually reversing the evolutionary process in which hellebores' true petals had been modified into nectaries; it is usually these nectaries which become the extra petals in double, semi-double and anemone-centred flowers. Double-flowered hellebores[14] provide a very interesting variation to the standard hellebore. They are generally easy to maintain and share the same planting conditions as the standard hellebore.

Semi-double flowers have one or two extra rows of petals; doubles have more. Their inner petals are generally very like the outer ones in colour and patterning. They are often of a similar length and shape, though they may be slightly shorter and narrower, and some are attractively waved or ruffled. By contrast, anemone-centred flowers have, cupped within the five normal outer petals, a ring of much shorter, more curved extra petals (sometimes trumpet-shaped, intermediate in appearance between petals and nectaries), which may be a different colour from the outer petals. These short, extra petals (sometimes known as "petaloids") drop off after the flower has been pollinated, leaving an apparently single flower, whereas doubles and semi-doubles tend to retain their extra petals after pollination.

Interspecific hybrids

Gardeners and nurserymen have also created hybrids between less closely related species. The earliest was probably H. × nigercors, a cross between H. niger and H. argutifolius (formerly H. lividus subsp. corsicus or H. corsicus, hence the name) first made in 1931. H. × sternii, a cross between H. argutifolius and H. lividus, first exhibited in 1947, is named after the celebrated British plantsman Sir Frederick Stern. H. × ballardiae (H. niger crossed with H. lividus) and H. × ericsmithii (H. niger crossed with H. × sternii) similarly commemorate the noted British nursery owners Helen Ballard and Eric Smith. In recent years, Ashwood Nurseries[15] (of Kingswinford in the English Midlands), already well known for its Ashwood Garden Hybrids[16] (H. × hybridus singles, semi-doubles, doubles and anemone-centres), has created hybrids between H. niger and H. thibetanus (called H. 'Pink Ice'), and between H. niger and H. vesicarius (called H. 'Briar Rose'). The gardenworthiness of these hybrids has still to be proven.

The following hellebore species and cultivars have gained the Royal Horticultural Society's Award of Garden Merit:

  • H. argutifolius[17]
  • H. foetidus[18]
  • H. lividus[19]
  • H. niger[20]
  • H. × sternii 'Blackthorn Group'[21]

Pests and diseases

Insects

Phytomyza hellebori

More commonly known as the Hellebore leaf miner, Phytomyza hellebori is a small fly that infests only the H. foetidus plants in the Hellebore family. The leaf miner fly digs tunnels into the leaves of the H. foetidus. The tunnels create brownish-black blotches on the plant. These will later turn into a nesting ground where the flies will lay their larvae in. The leaves will turn a brownish-white along where the tunnels were dug as time goes on. The larvae will start to eat the inside of the leaves in August, and damage will develop from the late summer to the early spring, with heavy attacks leaving the foliage disfigured by spring.[22]

To control heavy infestations, the leaves can be removed and destroyed during the winter months before the adult flies emerge. Insecticides can be used with limited effectiveness in controlling larvae and fly populations in the plant. Insecticides may harm non-leaf miner flies if applied during the hellebore's flowering period.[22]

Macrosiphum hellebori

Macrosiphum hellebori, commonly known as Hellebore aphid or greenfly, is a sap feeding aphid that infests the flowers and foliage of hellebore plants. The whitish-green aphids are about 2–4mm long and form dense colonies on hellebores, coating them with a honeydew that can lead to the growth of sooty mold on the leaves and flowers of the hellebore. This species of aphid only affects hellebores and is most active in March and April when the hellebores are flowering and when few aphid predators are around, though they may infest during any time of the year.[23][24]

Aphids will start their feeding from the outside the flowers, beginning at the leaves and then moving towards the flower petals of the hellebore. As the hellebore beings to open, the aphids will try to move into the flower. The aphids will then feed on the inner parts of the plant as well as the young stems and shoots. As the population grows, the aphids will eventually eat the remaining parts of the plant, such as older leaves, for food.[24]

Aphid infestations can be controlled through persistent squashing of the aphids manually, or by using insecticides. It is not recommended to spray flowering hellebores as it may harm the non-aphid pollinating insects.[23]

Diseases

Botrytis cinerea

Botrytis cinerea or grey mold is a fungal disease that infects most ornamental plants. The fungus causes a decay of plant tissues and will grow fuzzy gray-brown mold over the decaying areas, such as the buds, leaves, and flowers. Parts of the plant may shrivel and die after exposure to the mold, particularly the flowers. Typically the fungus will only infect plants through an open wound or when the plant is under stress, but it has also been known to infect plants in humid conditions. If the humidity is low the mold may be contained to discrete spots on the plant, but the mold has been known to spread rapidly in highly humid conditions. Grey mold can infect a plant at any time of the year and is not seasonally dependent. The fungus will form black seed like structures in the dead plant tissue to create its spores to help it survive when new host plants are scarce. The spores are spread through the air to new plants.[25]

To treat the infected plant, the first step is to remove infected and dying leaves, buds and flowers immediately along with any other dead plant materials around the hellebore. The next step is to reduce the humidity around the plant by improving the ventilation and ensuring the plants are not overcrowded.[25]

Coniothyrium hellebori

Coniothyrium hellebori is a fungus that causes the most common fungal disease for helleborus species known as Hellebore black spot or leaf spot. The disease is most common not only in botanical and ornamental gardens, but also in hellebore nurseries as well. Visible symptoms include blackish-brown spots that often appear as rings on the leaf blade or at the margins of the leaf. The spots will continue to grow larger as the disease progresses, retaining an elliptical or circular shape and turning a dark brown or black color. The spots will grow until they have infect the whole leaf. Petioles and flowers can also be infected, but the disease is primarily seen in the leaves. The symptoms become visible in the spring and worsen with time.[26]

The small black fruiting bodies which carry the spores, pycnidia, are formed in the dead cells of the leaf spots. The spores are mainly spread by water, wind and wind-blown rain. The fungus have an ideal habitat to spread and grow at the final growth site for hellebore plants and if left untreated the spores will remain for many years. The most effective method against C. hellebori is to remove and destroy the infected leaves immediately to avoid reinfection the following spring.[26][27]

Helleborus net necrosis virus

Helleborus net necrosis virus (HeNNV) also known as Hellebore black death is an RNA virus that can cause serious disease in Hellebore plants by stunting or deforming the plant as it grows. The disease marks the leaves of the hellebores with black streaks, often following the veins of the leaf, and creating ring patterns. It can also mark the sepals and flowers with black spots or streaks, but it will not always do so. When symptoms are severe new leaves will have limited growth before dying off.[28] The most seriously affected in the UK is Helleborus orientalis, but all hellebores are susceptible to the disease.[29] The most effective method of treatment against black death is to dig up and destroy all infected plants immediately. Many viruses are not transmitted through seeds, so it is possible to raise new disease resistant plants this way.[29]

Pseudomonas viridiflava

Pseudomonas viridiflava is a bacterium that has been claimed to cause disease in hellebores in New Zealand, among other plants. The bacterial disease manifested on hellebore plants in the form of black leaf spots, necrosis petal, and stem lesions. The most popular ornamental and commercial crop grown in New Zealand is Helleborus orientalis and its hybrids, of which 90 percent of the H. orientalis in the Tauranga nursery contracted the disease after several days of moderate rainfall. The disease caused discoloration in the form of black leaf spots that were circular and about 1.5–2mm in diameter, black stem lesions, and dry, grey to brown lesions with distinct margins on the flower petals. The symptoms were different from other leaf-spotting hellebore diseases, such as those caused by the fungus Coniothyrium and the bacteria Xanthomonas[30] The case in New Zealand is the only reported case of P. viridiflava infecting hellebores so far, but in other plants P. viridiflava has been reported to also induce symptoms such as leaf rot, leaf blotch, stem necrosis and blossom blight.[30]

Medicinal uses and toxicity

All helleborus plants are toxic, and all parts of the helleborus plant are toxic.[31][32] Hellebore poisoning is rare, but it does occur.[31] Hellebore plants are usually left alone by animals such as deer and rabbits due to the fact that the leaves of the plant produce poisonous alkaloids, making them distasteful to animals. The poisonous alkaloids have been known to sometimes bother gardeners with sensitive skin.[33]

Poisonings will occur through ingestion or handling. Hellebore plants should not be ingested as poisoning cases are most severe when the plants are eaten. This is especially true when hellebores are eaten in large quantities.[32] Symptoms of ingestion will include: burning of the mouth and throat, salivation, vomiting, abdominal cramping, diarrhea, nervous systems and possibly depression. Consuming large quantities of hellebore plants can be fatal.[32] Toxic cardiac glycosides occur in the roots. High levels of ranunculin and protoanemonin, especially in the leaves and sap, will also contribute to symptoms after ingestion.[31]

Dermatitis may also occur from handling the hellebore plants without protection. This is typically caused by the ranunculin and protoanemonin found on the outside of the plant, including areas such as the leaves, stem, flower, and sap. The poison on the outside of the plant will cause irritation and burning sensations on the skin.[31][32][34] When collecting seeds from hellebore plants it is recommended to wait for the pods to dry and shake them out into a container or onto the ground to collect. Attempts to remove the seeds by hand will expose skin to the potent toxins in the sap of the hellebore, which can increase the damage done to the skin.[34] Small or minimal exposure to the toxins should only cause a mild irritation to the skin, and the affliction should only last for a few minutes. If the burning persists or intensifies, it is recommended to wash the affected areas thoroughly to remove the toxins and see a doctor.[31][32][34]

In the early days of medicine, two kinds of hellebore were recognized: black hellebore, which included various species of Helleborus, and white hellebore, now known as Veratrum album,[35] which belongs to a different plant family, the Melanthiaceae.[36] Although the latter plant is highly toxic, containing veratrine and the teratogens cyclopamine (which can cause the fatal birth defect of cyclopia) and jervine, it is believed to be the "hellebore" used by Hippocrates as a purgative.

"Black hellebore" was used by the Greek and Romans to treat paralysis, gout and other diseases, more particularly insanity.[37] "Black hellebore" is also toxic, causing tinnitus, vertigo, stupor, thirst, anaphylaxis, emesis (vomiting), catharsis, bradycardia (slowing of the heart rate), and finally, collapse and death from cardiac arrest.[35] Although Helleborus niger (black hellebore) contains protoanemonin,[38] or ranunculin,[39] which has an acrid taste and can cause burning of the eyes, mouth, and throat, oral ulceration, gastroenteritis, and hematemesis,[40] research in the 1970s showed that the roots of H. niger do not contain the cardiotoxic compounds helleborin, hellebrin, and helleborein that are responsible for the lethal reputation of "black hellebore". It seems that earlier studies may have used a commercial preparation containing a mixture of material from other species such as Helleborus viridis, green hellebore.[39]

In folklore

Helleborus niger is commonly called the Christmas rose, due to an old legend that it sprouted in the snow from the tears of a young girl who had no gift to give the Christ child in Bethlehem.[41]

In Greek mythology, Melampus of Pylos used hellebore to save the daughters of the king of Argos from a madness, induced by Dionysus, that caused them to run naked through the city, crying, weeping, and screaming.[citation needed]

During the Siege of Kirrha in 585 BC, hellebore was reportedly used by the Greek besiegers to poison the city's water supply. The defenders were subsequently so weakened by diarrhea that they were unable to defend the city from assault.[42]

In a fit of madness induced by Hera, Heracles killed his children by Megara. His madness was cured using hellebore.[43]

  • Double hellebore, dark red
    Double hellebore, dark red
  • Double white and pink picotee hellebore
    Double white and pink picotee hellebore
  • Double pink hellebore with dark blotching
    Double pink hellebore with dark blotching
  • Double white hellebore with pink spotting
    Double white hellebore with pink spotting
  • Double pink hellebore with darker pink veining
    Double pink hellebore with darker pink veining
  • Double white hellebore hybrid 'Betty Ranicar'
    Double white hellebore hybrid 'Betty Ranicar'
  • Yellow double hellebore
    Yellow double hellebore
  • "Blue-black" double hellebore
    "Blue-black" double hellebore
  • Double pink hellebore with dark venation
    Double pink hellebore with dark venation
  • Seed pods swell.
    Seed pods swell.
  • Helleborus bocconei
    Helleborus bocconei
  • Helleborus dumetorum (Hecken-Nieswurz)
    Helleborus dumetorum (Hecken-Nieswurz)
  • Helleborus lividus ssp. corsicus (Jardin des Plantes de Paris)
    Helleborus lividus ssp. corsicus (Jardin des Plantes de Paris)
  • Helleborus foetidus
    Helleborus foetidus
  • Helleborus odorus (Ranunculaceae) plant
    Helleborus odorus (Ranunculaceae) plant
  • Helleborus purpurascens
    Helleborus purpurascens
  • Helleborus argutifolius - Innsbruck Botanical Garden
    Helleborus argutifolius - Innsbruck Botanical Garden
  • Helleborus niger with flowers in two different stages, and fruits
    Helleborus niger with flowers in two different stages, and fruits

References

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  2. ^ "Definition of HELLEBORE". www.merriam-webster.com.
  3. ^ a b "Hellebores' roses of winter - Yates". www.yates.co.nz.
  4. ^ "Christmas Rose". Retrieved 18 June 2014.
  5. ^ "Helleborus niger - Christmas Rose". Retrieved 9 June 2014.
  6. ^ Bailly, Anatole (1 January 1981). Abrégé du dictionnaire grec français. Paris: Hachette. ISBN 978-2010035289. OCLC 461974285.
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  8. ^ "Archived copy". Archived from the original on 24 July 2014. Retrieved 18 July 2014.{{cite web}}: CS1 maint: archived copy as title (link)
  9. ^ "Nursery owner extols many virtues of hellebores". Archived from the original on 28 May 2014. Retrieved 28 May 2014.
  10. ^ "Helleborus Walberton's Rosemary='Walhero'". www.rhs.org. Royal Horticultural Society. Retrieved 6 August 2020.
  11. ^ a b c d Julia Meiners; Thomas Debener; Guenther Schweizer; Traud Winkelmann (2011). "Analysis of the taxonomic subdivision within the genus Helleborus by nuclear DNA content and genome-wide DNA markers". Scientia Horticulturae. 128 (1): 38–47. doi:10.1016/j.scienta.2010.12.011.
  12. ^ Klaus Werner; Friedrich Ebel (1994). "Zur Lebensgeschichte der Gattung Helleborus L. (Ranunculaceae)". Flora. 189: 97–130. doi:10.1016/S0367-2530(17)30578-9.
  13. ^ Walter K. Rottensteiner (2016). "Attempt of a morphological differentia tion of Helleborus species in the Northwestern Balkans". Modern Phytomorphology. 9(Suppl.): 17–33. doi:10.5281/zenodo.159701.
  14. ^ "Double Hellebores". Retrieved 9 October 2007.
  15. ^ "ashwoodnurseries.com". ashwoodnurseries.com. Retrieved 2 August 2012.
  16. ^ "Hellebores: Ashwood Garden Hybrids". Ashwoodnurseries.com. Retrieved 2 August 2012.
  17. ^ "RHS Plant Selector Helleborus argutifolius AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2 August 2012.
  18. ^ "RHS Plant Selector Helleborus foetidus AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2 August 2012.
  19. ^ "RHS Plant Selector Helleborus lividus AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2 August 2012.
  20. ^ "RHS Plant Selector Helleborus niger AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2 August 2012.
  21. ^ "RHS Plant Selector Helleborus × sternii Blackthorn Group AGM / RHS Gardening". Apps.rhs.org.uk. Retrieved 2 August 2012.
  22. ^ a b "Hellebore leaf miner". Royal Horticulture Society.
  23. ^ a b "Hellebore Aphid". Royal Horticultural Society.
  24. ^ a b Valenzuela, Isabel; Carver, Mary; Malipatil, Mallik B; Ridland, Peter M (May 2009). "Occurrence of Theobald & Walton (Hemiptera: Aphididae) in Australia". Australian Journal of Entomology. 48 (2): 125–129. doi:10.1111/j.1440-6055.2009.00696.x.
  25. ^ a b "Grey Mould". Royal Horticulture Society.
  26. ^ a b Meiners, Julia; Winkelmann, Traud (October 2011). "Morphological and Genetic Analyses of Hellebore Leaf Spot Disease Isolates from Different Geographic Origins Show Low Variability and Reveal Molecular Evidence for Reclassification into Didymellaceae". Journal of Phytopathology. 159 (10): 665–675. doi:10.1111/j.1439-0434.2011.01823.x.
  27. ^ Gluecksohn-Waelsch, S; Schiffman, MB (August 1975). "Glutamine synthetase in newborn mice homozygous for lethal albino alleles". Developmental Biology. 45 (2): 369–71. doi:10.1016/0012-1606(75)90075-5. ISSN 0269-915X. PMID 269.
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Notes

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