Earth and Space News: November to February flowering hellebores

Showing posts with label November to February flowering hellebores. Show all posts

Sunday, February 12, 2017

Helleborus ‘HGC Merlin’ Has Dark Purple Flowers and Dark Green Leaves

Summary: Helleborus ‘HGC Merlin,’ a Lenten rose (Helleborus orientalis) cultivar by German breeder Joseph Heuger, has dark purple flowers and dark green leaves.

side view of flower of Helleborus ‘HGC Merlin’ in images included in Joseph Heuger’s patent application, filed Monday, June 28, 2004, as application number 10/878415, with the United States Patent and Trademark Office (USPTO); United States Plant Patent No. US PP15,705; Date of Patent March 29, 2005; color scans via Plant Patents Image Database, Digital Collections @ University of Maryland Libraries

Helleborus ‘HGC Merlin,’ a Lenten rose (Helleborus orientalis) cultivar by German hellebore hybridizer Joseph Heuger, has dark purple flowers and dark green leaves.

On June 28, 2004, Heuger filed an application with the United States Patent and Trademark Office for a patent for Helleborus orientalis ‘HGC Merlin.’ Primary examiner Kent Bell and assistant examiner Wendy C. Haas reviewed Heuger’s application. On March 29, 2005, the U.S. Patent and Trademark Office assigned plant patent number 15,705 to Helleborus ‘HGC Merlin.’

‘HGC Merlin’ has its origins in a breeding program conducted in January 1999 by Heuger. Unnamed, unpatented female and male Helleborus orientalis seedlings were cross-pollinated in a controlled environment at Heuger’s family nursery, Heuger Gartenbaubetriebe, in Glandorf, Lower Saxony state, northwestern Germany.

Heuger discovered and selected the flowering plant now known as ‘HGC Merlin’ from among the cross-pollinated parents’ offspring. ‘HGC Merlin’ displayed distinguishing traits of a mounded, upright habit; attractive flower and leaf colorings; relatively early and long blooming period. Propagation by divisions, begun in March 2001, confirmed the retention and true reproduction of the new cultivar’s distinguishing traits over successive generations.

Heuger’s application describes 6-month-old plants that were grown in 15-centimeter (5.9-inch) containers during winter. Production temperatures in the Heuger nursery’s glass-covered greenhouse were about 18 degrees Celsius (64.4 degrees Fahrenheit) during the day and about 14 degrees C (57.2 degrees F) during the night.

Helleborus ‘HGC Merlin’ has a temperature tolerance that ranges from minus 12 to 36 degrees C (10.4 to 96.8 degrees F).

‘HGC Merlin’ has a moderately vigorous growth habit. The new cultivar’s upright, mounded form includes basal leaves and single flowers. Height measures about 20 centimeters (7.87 inches). Spread, or width, is about 40 centimeters (15.74 inches).

Basal leaves are palmately compound. Five to seven leaflets radiate from each leaf’s petiole, the leaf stalk that attaches the leaf to the stem.

Lanceolate, or lance-shaped, leaves have serrated margins. Glabrously textured upper and lower surfaces are hairlessly smooth.

Upper surfaces of fully expanded leaflets are dark green (Royal Horticultural Society colour chart color 147A). Veins are brown green (RHS 146B to 146C).

Lower surfaces of fully expanded leaves are brown green (RHS 147B). Veins are brown green (RHS 146C).

Helleborus ‘HGC Merlin’ has a relatively early and lengthy natural flowering season. Intermittent flowering occurs from November to February in Glandorf. A freely flowering habit yields about 10 developing flowers per plant over the blooming period. On the plant, flowers last about 10 days.

The cultivar’s single rounded flowers are each borne in a single arrangement on short peduncles, or floral stems. Each plant typically has more than one peduncle.

Ovoid, or egg-shaped, buds have a height of about 1.4 centimeters (0.55 inches). Bud diameter is about 1.1 centimeters (0.43 inches). Coloring is between dark violet (RHS 79A) and brown purple (RHS 187A).

Flowers droop outwardly. ‘HGC Merlin’ has no detectable fragrance.

Petals are tiny and form inconspicuous nectaries. Sepals, typically numbering five, are arranged as a single whorl for each flower. Sepal length is about 3.5 centimeters (1.37 inches). Sepal width is about 3.3 centimeters (1.29 inches).

Broadly ovate, or egg-shaped, sepals have smooth, untoothed margins, described as entire. Upper and lower surfaces have a glabrous texture that is satiny and hairlessly smooth.

Upper and lower surfaces of developing and fully expanded sepals are between dark violet (RHS 79A) and brown purple (RHS 187A).

Peduncles are strong, with a straight to bent orientation. Length range is from about 3 to 5 centimeters (1.18 to 1.96 inches). Peduncle diameter is about 1.5 millimeters (0.059 inches). Glabrously textured peduncles are hairlessly smooth. Colorings is brown green (RHS 146C), with an overlay of dark purple red (RHS 187C).

Heuger’s 2015-2016 hellebore catalog lists ‘HGC Merlin’®℗ as available in containers sized 15 to 19 centimeters (5.90 to 7.48 inches). Growth is described as vigorous. Heating, at a maximum temperature of 14 degrees C (57.2 degrees F), is slated for the end of January. The beginning of February is targeted as selling start date.

The takeaway for Helleborus ‘HGC Merlin’ is the winter interest of the Lenten rose cultivar’s showy dark purple flowers, in fresh cut arrangements and in in-ground and potted garden niches, throughout a relatively early and long flowering season that begins in late autumn and lasts throughout winter.

closeup of Helleborus ‘HGC Merlin’ flower in images included in Joseph Heuger’s patent application, filed Monday, June 28, 2004, as application number 10/878415, with the United States Patent and Trademark Office (USPTO); United States Plant Patent No. US PP15,705; Date of Patent March 29, 2005; color scans via Plant Patents Image Database, Digital Collections @ University of Maryland Libraries

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Burrell, C. Colston; Judith Knott Tyler. Hellebores: A Comprehensive Guide. Portland OR: Timber Press, 2006.

Burrell, C. Colston; Judith Knott Tyler. “Not Your Mother’s Hellebores: A New Look at Species and Hybrids (Part 2).” Pacific Horticulture magazine. January 2008.
Available @ http://www.pacifichorticulture.org/articles/not-your-mothers-hellebores-part-2/

“Hellebore (Helleborus Gold Collection® Merlin).” The National Gardening Association > Plants Database > Hellebores.
Available @ http://garden.org/plants/view/586946/Hellebore-Helleborus-Gold-Collection-Merlin/

“Helleborus Plant Named ‘HGC Green Corsican.’” United States Patent and Trademark Office > Program in Word (PIW). March 8, 2005.
Available @ http://pdfpiw.uspto.gov/.piw?PageNum=0&docid=PP015641

“HGC Merlin’®℗.” Heuger > Katalog Helleborus 2015-2016.
Available @ http://www.heuger.com/fileadmin/lookbook/page5.html#/34

International Union for the Protection of New Varieties of Plants. “Document TGP/14: Glossary of Technical, Botanical and Statistical Terms Used in UPOV Documents. Section 2: Botanical Terms: Subsection 3: Color: (2): Color Names for the RHS Colour Chart.” UPOV (Union Internationale Pour la Protection des Obtentions Végétales). Dec. 9, 2006.
Available @ http://www.upov.int/edocs/mdocs/upov/en/tc_edc?2007/tgp_14_draft_1_section_2_3_2.pdf

Marriner, Derdriu. “Helleborus ‘COSEH 210’ Has Large White Flowers and Sells as ‘HGC Joel’®.” Earth and Space News. Sunday, Jan. 8, 2017.
Available @ https://earth-and-space-news.blogspot.com/2017/01/helleborus-coseh-210-has-large-white.html

Marriner, Derdriu. “Helleborus ‘COSEH 710’ Has Light Green Flowers With Reddish Pink Flushes.” Earth and Space News. Sunday, Nov. 13, 2016.
Available @ https://earth-and-space-news.blogspot.com/2016/11/helleborus-coseh-710-has-light-green.html

Marriner, Derdriu. “Helleborus ‘COSEH 740’ Has White Flowers and Dark Green Leaves.” Earth and Space News. Saturday, Nov. 26, 2016.
Available @ https://earth-and-space-news.blogspot.com/2016/11/helleborus-coseh-740-has-white-flowers.html

Marriner, Derdriu. “Helleborus ‘HGC Double Surprise’ Has Purple-Spotted White Double Flowers.” Earth and Space News. Sunday, Jan. 22, 2017.
Available @ https://earth-and-space-news.blogspot.com/2017/01/helleborus-hgc-double-surprise-has.html

Marriner, Derdriu. “Helleborus ‘HGC Jericho’ Has Large White Flowers and Dark Green Leaves.” Earth and Space News. Sunday, Feb. 5, 2017.
Available @ https://earth-and-space-news.blogspot.com/2017/02/helleborus-hgc-jericho-has-large-white.html

Marriner, Derdriu. “Helleborus ‘HGC Josef Lemper’ Has White Flowers and Dark Green Leaves.” Earth and Space News. Saturday, Jan. 28, 2017.
Available @ https://earth-and-space-news.blogspot.com/2017/01/helleborus-hgc-josef-lemper-has-white.html

Marriner, Derdriu. “Helleborus ‘HGC Lady Freckle’ Has Red Purple-Spotted White Flowers.” Earth and Space News. Sunday, Jan. 29, 2017.
Available @ https://earth-and-space-news.blogspot.com/2017/01/helleborus-hgc-lady-freckle-has-red.html

Marriner, Derdriu. “Helleborus ‘HGC Silvermoon' Has White to Light Green Flowers.” Earth and Space News. Saturday, Feb. 4, 2017.
Available @ https://earth-and-space-news.blogspot.com/2017/02/helleborus-hgc-silvermoon-has-white-to.html

Marriner, Derdriu. “A Helleborus Plant Named ‘COSEH 700’ Has Large Light Green Flowers.” Earth and Space News. Saturday, Nov. 12, 2016.
Available @ https://earth-and-space-news.blogspot.com/2016/11/a-helleborus-plant-named-coseh-700-has.html

Marriner, Derdriu. “A Helleborus Plant Named ‘HGC Jacob’ Has White to Light Green Flowers.” Earth and Space News. Sunday, Nov. 6, 2016.
Available @ https://earth-and-space-news.blogspot.com/2016/11/a-helleborus-plant-named-hgc-jacob-has.html

“PP15705 -- Helleborus Plant Named ‘HGC Merlin.’” University of Maryland > Plant Patents Image Database.
Available @ http://www.lib.umd.edu/plantpatents/id/11671

Rice, Graham; Elizabeth Strangman. The Gardener’s Guide to Growing Hellebores. Newton Abbot, England: David and Charles, 2005.

Sunday, January 29, 2017

Helleborus ‘HGC Lady Freckle’ Has Red Purple-Spotted White Flowers

Summary: Helleborus ‘HGC Lady Freckle,’ a Lenten rose (Helleborus orientalis) variety by German hybridizer Joseph Heuger, has red purple-spotted white flowers.

side view of flower of Helleborus ‘HGC Lady Freckle’ in images included in Joseph Heuger’s patent application, filed Monday, June 28, 2004, as application number 10/878416, with the United States Patent and Trademark Office (USPTO); United States Plant Patent No. US PP15,618; Date of Patent March 1, 2005; color scans via Plant Patents Image Database, Digital Collections @ University of Maryland Libraries

Helleborus ‘HGC Lady Freckle,’ a Lenten rose (Helleborus orientalis) variety by German hellebore hybridizer Joseph Heuger, has red purple-spotted white flowers.

On June 28, 2004, Heuger filed an application with the United States Patent and Trademark Office for a patent for Helleborus ‘HGC Lady Freckle.’ Primary examiner Kent Bell and assistant examiner Wendy C. Haas reviewed Heuger’s application. On March 1, 2005, the U.S. Patent and Trademark Office assigned plant patent number 15,618 to Helleborus ‘HGC Lady Freckle.’

Helleborus ‘HGC Lady Freckle’ has its origins in a breeding program established in January 1999 by Joseph Heuger at his family’s nursery, Heuger Gartenbaubetriebe, in Glandorf, Lower Saxony state, northwestern Germany. Unnamed, unpatented female and male Helleborus orientalis seedlings were cross-pollinated in a controlled environment. The inventor discovered and selected the flowering plant now known as Helleborus ‘HGC Lady Freckle’ from among the cross-pollinated parents’ offspring.

The new variety displayed distinctive traits, such as attractive flower and leaf colorations; a mounded, upright habit; relatively early flowering. Propagation by divisions, begun in March 2001, confirmed the retention and true reproduction of the new cultivar’s unique features over successive generations.

Heuger’s patent application describes plants, at about 6 months of age, grown indoors in 15-centimeter (5.90-inch) containers during winter. During production, the day temperature in the glass-covered greenhouse in Glandorf registered about 18 degrees Celsius (64.4 degrees Fahrenheit). The night temperature was about 14 degrees C (57.2 degrees F).

Helleborus ‘HGC Lady Freckle’ has a temperature tolerance that ranges from minus 12 to 36 degrees C (10.4 to 96.8 degrees F).

The new cultivar’s moderately vigorous growth yields a mounded, upright plant habit, with basal leaves and single flowers. Plant height measures about 25 centimeters (9.84 inches). Width, or spread, measures about 40 centimeters (15.748 inches).

Basal foliage is palmately compound. Five to six leaflets radiate from the leaf’s single attachment point at the distal, or far, end of the petiole, or leaf stalk.

Leaflet lengths range from 6 to 9.5 centimeters (2.36 to 3.74 inches). Widths range from about 2.2 to 3.5 centimeters (0.86 to 1.37 inches).

Lanceolate, or lance-shaped, leaflets have serrated margins. Glabrous surface textures are hairlessly smooth.

Upper surfaces of fully expanded leaflets are dark green (Royal Horticultural Society colour chart color 147A). Lower surfaces are brown green (RHS 147B). Venation of upper and lower surfaces is brown green (RHS 146D).

Helleborus ‘HGC Lady Freckle’ has a relatively early and long natural blooming period. Intermittent flowering stretches from November to February in Glandorf. On the plant, flowers last about 10 days.

The new variety’s floral type and habit reveal single, outwardly drooping, rounded flowers, each in a single arrangement on short peduncles, or floral stems. Peduncles are about 4.5 centimeters (1.77 inches) in length, with a diameter of about 2 millimeters (0.07 inches).

Despite their bent orientation, peduncles are moderately strong. Their glabrous texture is hairlessly smooth. Coloring is light green (RHS 145A).

A freely flowering habit encourages about 15 developed flowers per plant over the blooming period. Typically each plant has more than one flowering stem.

Ovoid, or egg-shaped, flower buds measure a diameter of about 1 centimeter (0.39 inches) and a height of about 1.5 centimeters (0.59 inches). Bud coloring is light green (RHS 145C to 145D).

Flowers have minute petals that form inconspicuous nectaries. Sepals typically number five per flower, forming a single whorl.

Sepal length and width have identical measurements. Sepals measure 3 centimeters (1.18 inches) in length and also in width.

Broadly ovate, or egg-shaped, sepals have smooth, untoothed margins, described as entire. Glabrous upper and lower surface textures are hairlessly and satiny smooth.

Upper and lower surfaces of developing and fully expanded sepals are white (RHS 155C). Spots toward the center of upper surfaces are dark purple red (RHS 59B).

The takeaway for Helleborus ‘HGC Lady Freckle’ is the lengthy opportunities, via the new Heuger hellebore’s early and extensive blooming period, for enjoyment of red purple-spotted white flowers that top light green floral stems and contrast attractively with dark green leaves.

closeup of Helleborus ‘HGC Lady Freckle’ flower in images included in Joseph Heuger’s patent application, filed Monday, June 28, 2004, as application number 10/878416, with the United States Patent and Trademark Office (USPTO); United States Plant Patent No. US PP15,618; Date of Patent March 1, 2005; color scans via Plant Patents Image Database, Digital Collections @ University of Maryland Libraries

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Burrell, C. Colston; Judith Knott Tyler. Hellebores: A Comprehensive Guide. Portland OR: Timber Press, 2006.

“Helleborus Plant Named ‘HGC Lady Freckle.’” United States Patent and Trademark Office > Program in Word (PIW). March 1, 2005.
Available @ http://pdfpiw.uspto.gov/.piw?PageNum=0&docid=PP015618

Marriner, Derdriu. "Helleborus ‘HGC Josef Lemper’ Has White Flowers and Dark Green Leaves." Earth and Space News. Saturday, Jan. 28, 2017.
Available @ https://earth-and-space-news.blogspot.com/2017/01/helleborus-hgc-josef-lemper-has-white.html

“PP15618 -- Helleborus Plant Named ‘HGC Lady Freckle.’” University of Maryland > Plant Patents Image Database.
Available @ http://www.lib.umd.edu/plantpatents/id/11584

Rice, Graham; Elizabeth Strangman. The Gardener’s Guide to Growing Hellebores. Newton Abbot, England: David and Charles, 2005.

Sunday, December 25, 2016

Helleborus ‘HGC Joshua’ Has White to Light Green Flowers

Summary: Helleborus ‘HGC Joshua,’ a Christmas rose (Helleborus niger) cultivar by German breeder Joseph Heuger, has white to light green flowers.

side view of flower of Helleborus ‘HGC Joshua’ in images included in Joseph Heuger’s patent application, filed Friday, Feb. 17, 2006, as application number 11/358858, with the United States Patent and Trademark Office (USPTO); United States Plant Patent No. US PP17,957; Date of Patent Aug. 28, 2007; color scans via Plant Patents Image Database, Digital Collections @ University of Maryland Libraries

Helleborus ‘HGC Joshua,’ a Lenten rose, or black hellebore (Helleborus orientalis), cultivar by German hellebore hybridizer Joseph Heuger, has white to light green flowers and dark green leaves.

On Feb. 17, 2006, Heuger filed an application with the United States Patent and Trademark Office for a patent for Helleborus ‘HGC Joshua.’ Primary examiner Kent Ball and assistant examiner Annette H. Para reviewed Heuger’s application. On Aug. 28, 2007, the U.S. Patent and Trademark Office assigned plant patent number 17,957 to Helleborus ‘HGC Joshua.’

‘HGC Joshua’ has its origins in a breeding program conducted in December 1999 by the inventor. Unnamed, unpatented female and male Helleborus niger seedlings were cross-pollinated in a controlled environment at Heuger’s family nursery, Heuger Gartenbaubetriebe, in Glandorf, Lower Saxony state, northwestern Germany.

Heuger discovered and selected the flowering plant now known as Helleborus ‘HGC Joshua’ from among the cross-pollinated parents’ progeny. ‘HGC Joshua’ exhibited distinctive traits of a compact, upright habit; attractively colored flowers and leaves; an early and long flowering season.

Heuger’s application describes approximately 1-year-old plants that were grown in 13-centimeter (5.11-inch) containers in a glass-covered greenhouse in winter and in an outdoor summer nursery. Production temperatures in the greenhouse registered about 12 degrees Celsius (53.6 degrees Fahrenheit) during the day and ranged from about 2 degrees to about 12 degrees C (35.6 to 53.6 degrees F) during the night. Temperatures in the outdoor nursery ranged from about 5 to 34 degrees C (41 to 93.2 degrees F) during the day and from about 1 to about 25 degrees C (33.8 to 77 degrees F) during the night.

When planted in the ground, Helleborus ‘HGC Joshua’ has a temperature tolerance that ranges from about minus 10 to about 36 degrees C (14 to 96.8 degrees F).

Heuger’s Helleborus niger cultivar displays a moderately vigorous growth habit. Its compact, upright form features basal leaves and single flowers. Height ranges are from about 8 to 12 centimeters (3.14 to 4.72 inches). Spread, or width, ranges from about 20 to 25 centimeters (7.87 to 9.84 inches).

Basal foliage is palmately compound. Five to seven leaflets radiate from each leaf’s petiole, the stalk attaching the leaf to the stem.

Lanceolate, or lance-shaped, leaflets have serrated margins. Upper and lower surfaces have textures described hairlessly smooth, or glabrous, and leathery.

Leaflet length ranges from about 3.5 to 6 centimeters (1.37 to 2.36 inches). Width range is from about 1.5 to 3 centimeters (0.59 to 1.18 inches).

Upper surfaces of developing and fully expanded leaflets are dark green (close to Royal Horticultural Society colour chart color 147A). Veins are brown green (RHS 146B).

Lower surfaces of developing and fully expanded leaflets are brown green (close to RHS 147B). Veins are brown green (RHS 146C).

Petioles have lengths of about 1 to 8 millimeters (0.039 to 0.314 inches). Diameter range is from about 2 to 2.5 millimeters (0.078 to 0.098 inches).

Upper and lower surfaces of petioles are hairlessly smooth, described as glabrous.

Upper and lower surfaces of petioles are brown green (RHS 146C to 146D). Random spots are dark brown (RHS 200A to 200B).

Helleborus ‘HGC Joshua’ has an early and long natural flowering season. Intermittent flowering occurs from November to February in Germany. A freely flowering habit yields about 10 to 15 developing flowers per plant over the blooming period. On the plant, flowers last about 10 days.

Single rounded flowers are each borne in a single arrangement on upright peduncles, or floral stems. Flowers have a slight fragrance and mostly face uprightly to outwardly.

Ovoid, or egg-shaped, buds are about 1.2 centimeters (0.47 to inches) in height. Bud diameter is about 8 centimeters (3.14 inches).

Each flower typically comprises five to eight sepals, arranged in a single whorl. Sepal length ranges from about 2.5 to 3 centimeters (0.98 to 1.18 inches). Sepal width is about 2 centimeters (0.78 inches).

Broadly ovate, or egg-shaped, sepals have smooth margins, described as entire. Textures of upper and lower surfaces are described as glabrous, with hairless smoothness, and satiny.

Upper and lower surfaces of fully expanded sepals are bright white (more than RHS 155D), with light green (RHS 144C) toward the base. With development, coloring approaches light green (close to RHS 144B to 144C).

Peduncles are strong, with a mostly upright orientation. Peduncle texture is hairlessly smooth, described as glabrous.

Peduncle length ranges from about 10 to 25 centimeters (3.93 to 9.84 inches). Diameter range is from about 2 to 5 millimeters (0.078 to 0.19 inches).

Peduncle coloring is light green (RHS 145B), with brown purple (RHS 178A) spots.

Heuger’s 2015-2016 hellebore catalog lists ‘HGC Joshua’℗ as available in containers sized 11 to 13 centimeters (4.33 to 5.11 inches). Growth is described as compact. Selling is targeted to begin in mid-November.

The takeaway for Helleborus ‘HGC Joshua’ is the early, long blooming period, from late autumn through winter, that Heuger’s Christmas rose cultivar enjoys and the pleasing colors that Joshua’s white to light green flowers and dark green leaves contribute to fresh cut arrangements and to in-ground and potted garden spaces.

Helleborus Joshua, German hellebore hybridizer Joseph Heuger's Christmas rose cultivar, shows well in floral displays: CowellsGardenCentre @CowellsgCentre, via Twitter Dec. 11, 2011

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Helleborus Joshua, German hellebore hybridizer Joseph Heuger's Christmas rose cultivar, shows well in floral displays: CowellsGardenCentre @CowellsgCentre, via Twitter Dec. 11, 2011, @ https://twitter.com/CowellsgCentre/status/145810543641493504

For further information:

Burrell, C. Colston; Judith Knott Tyler. Hellebores: A Comprehensive Guide. Portland OR: Timber Press, 2006.

CowellsGardenCentre @CowellsgCentre. "A canny cracking Christmas combo - Skimmia 'Temptation' & Helleborus 'Joshua.' Twitter. Dec. 11, 2011.
Available @ https://twitter.com/CowellsgCentre/status/145810543641493504

“Hellebore (Helleborus niger Gold Collection® Joshua).” The National Gardening Association > Plants Database > Hellebores.
Available @ http://garden.org/plants/view/586778/Hellebore-Helleborus-niger-Gold-Collection-Joshua/

“Helleborus Plant Named ‘HGC Joshua.’” United States Patent and Trademark Office > Program in Word (PIW). Aug. 28, 2007.
Available @ http://pdfpiw.uspto.gov/.piw?PageNum=0&docid=PP017957

“HGC Joshua’℗.” Heuger > Katalog Helleborus 2015-2016.
Available @ http://www.heuger.com/fileadmin/lookbook/page5.html#/14

“PP17957 -- Helleborus Plant Named ‘HGC Joshua.’” University of Maryland > Plant Patents Image Database.
Available @ http://www.lib.umd.edu/plantpatents/id/13922

Rice, Graham; Elizabeth Strangman. The Gardener’s Guide to Growing Hellebores. Newton Abbot, England: David and Charles, 2005.