Helleborus species and their distribution

HELLEBORUS SPECIES

Helleborus, with its various different species, belongs to the buttercup family (Ranunculaceae), along with other popular genera, such as clematis (Clematis), delphinium (Delphinium) and globeflower (Trollius).

Distribution of the Helleborus genus of approximately 20 species is limited to the northern hemisphere including Europe and Asia. Some species are very distant from each other in terms of both descent and properties.

Classification according to B. Mathew

Brian Mathew divided the Helleborus species into six groups in 1989. The classification is based on the following – usually morphological – parameters:

- type of growth (presence or absence of stem)

- properties of leaves and seeds (carpels grown together or separate, anther shape and properties, seed size and shape)

- differences in the leaf and flower colours

- habitat requirements

- ability to hybridise

Classification according to B. Mathew

1. Syncarpus:	2. Griphopus:	3. Chenopus:	4. Helleborus:	5. Helleborastrum:	6. Dicarpon:
H. vesicarius	H. foetidus	H. argutifolius	H. niger	H. abruzzicus	H. thibetanus
		H. lividus		H. atrorubens
				H. bocconei
				H. croaticus
				H. cyclophyllos
				H. dumetorum
				H. hercegovinus
				H. istriacus
				H. liguricus
				H. multifidus
				H. occidentalis
				H. orientalis
				H. purpurascens
				H. torquatus
				H. viridis

Stemmed and stemless species

Helleborus species are generally classified into two groups, the stemmed (caulescent) and the stemless (acaulescent) species. The difference between these two groups is that the caulescent plants grow stems above ground-level, whereas the acaulescent do not.

Another difference is in the root system, the so-called rhizome. In the stemless species, flowers and leaves are grown separately from the woody rhizomes and the plant height seldom reaches more than 45 cm. The acaulescent species are very long-lived, reaching an age of up to 25 years in optimal habitat conditions. This group includes most Helleborus species and the Lenten Roses.

In stemmed species, leaves and flowers grow from upright, woody shoots. Unlike the acaulescent species, the caulescent species cannot be propagated by division. They seldom reach more than 2 to 4 years of age and can grow to a height of up to 120 cm. The stems die after having produced seed. There are three caulescent species and today also a number of interspecific crosses that belong to this group.

The Christmas Rose (Helleborus niger) is in a category all of its own. It is an acaulescent species in the sense that is does not produce stems above the ground. However, in other aspects it differs from the other species in the group.

The following table, complemented by C. Colston Burrell and Judith Knott Tylor (2006), lists the three types and the species allocated to them.

HELLEBORUS CROSSES

Acaulescent	Acaulescent/Caulescent	Caulescent	Artkreuzungen
H. abruzzicus	H. niger	H. argutifolius	H. x ericsmithii
H. atrorubens		H. foetidus	H. x ballardiae
H. bocconei		H. lividus	H. x nigercors
H. cyclophyllos			H. x hybridus
H. dumetorum			H. x lemperii
H. hercegovinus			H. x glandorfensis
H. istriacus			H. x iburgensis
H. liguricus
H. occidentalis
H. odorus
H. orientalis
H. purpurascens
H. thibetanus
H. viridis
H. torquatus
H. vesicarius

HELLEBORUS CROSSES

A number of hybrids have also been created through natural or intentional crossings between various Helleborus species.

Lenten Roses (H. x hybrida) are hybrids between H. orientalis and other acaulescent species. They are often called "H. orientalis hybrids", which is incorrect.

The caulescent hybrids include the following:

- H. x sternii: hybrid of H. lividus and H. argutifolius

- H. x ericsmithii: hybrid of H. x sternii and H. niger

- H. x nigercors: hybrid of H. argutifolius and H. niger

- H. x ballardiae: hybrid of H. lividus and H. niger

- H. x jourdanii: hybrid of H. foetidus and H. viridis

- H. x lemonnierae: cross partner unknown

- H. x glandorfensis: hybrid of H. x ericsmithii x H. x hybridus

- H. x sahinii: hybrid of H. niger x H. Helleborus foetidus

- H. x belcherii: hybrid of H. niger x H. Helleborus thibetanus

- H. x iburgensis: hybrid of H. x ballardiae x H. x hybridus

Distribution

In the course of geological shifts, the predecessors of today's Helleborus species probably spread west from Southeast Asia, along the ancient Mediterranean Sea. As warm and cold periods alternated during that time, hellebores developed the ability to delay, or even interrupt, their growth and flowering period. Another remainder of that time is their more or less strong ability to lower the pressure inside their cells in response to frost. This effect can be reversed as temperatures rise. You can observe this phenomenon quite well on a morning after a frosty night when the leaves and flowers are bent towards the ground and, as the day unfolds and temperatures climb, gradually rise back to their upright positions.

Distribution of the Helleborus genus is limited to the northern hemisphere including Europe and Asia. Helleborus species are most highly concentrated along the Mediterranean Sea, but some species are also native to places along the Black Sea coasts.

Only the origins of the two species Helleborus vesicarius and Helleborus thibetanus are different. Helleborus vesicarius grows in the border region between Syria and Turkey. Helleborus thibetanus is native to China.