Ivy Broomrape

''Orobanche hederae'', the ivy broomrape, is, like other members of the genus ''Orobanche'', a parasitic plant without chlorophyll, and thus totally dependent on its host, which is ivy. It grows to , with stems in shades of brown and purple, sometimes yellow. The flowers are long, cream in colour with reddish-purple veins.

Etymology

''Orobanche'' is derived from Greek, and means 'bitter vetch strangler' or 'legume strangler'. This name originates from the species ''Orobanche rapum-genistae'', which parasitizes legumes. The name ''hederae'' means 'of ivy', in reference to its host plant, ''Hedera''.

Its common name in English is ''ivy broomrape''. It is also called ''frare de l'heura'' in Catalan, ''bršljanov volovod'' in Croatian, ''záraza břečťanová'' in Czech, ''vedbend-gyvelkvæler'' in Danish, ''klimopbremraap'' in Dutch, ''orobanche du lierre'' in French, ''klimmerblêdfretter'' in Frysk, ''efeuwürger'' and ''efeu-sommerwurz'' in German, ''borostyán-vajvirág'' in Hungarian, ''múchóg'' or ''múchóg mhór'' in Irish, ''succiamele dell'edera'' in Italian, ''bergflette-snylterot'' in Norwegian, ''erva-toira da hera'' or ''erva-toira'' in Portuguese, ''заразиха плющевая'' in Russian, ''záraza brečtanová'' in Slovak, ''pojalnik bršljanov'' in Slovene, ''espárrago de lobo'', ''jopo de la hiedra'', ''jopo espárrago de lobo'', or ''matalegumbre'' in Spanish, ''murgrönssnyltrot'' in Swedish, ''tez canavarotu'' in Turkish, and ''gorfanc eiddew'' or ''gorfanhadlen eiddew'' in Welsh.

Description

Its yellowish to purplish stems are usually strongly swollen at the base and by . They are covered in short soft glandular hairs. Leaves are acute and oblong to lance-shaped. Its calyx (sepals) are with free segments that are entire or unequally bifid. Its dull-cream to reddish purple corolla (petals) is . They are almost hairless and upright spreading to more or less patent. Filaments (stalks of the stamen) are inserted above the base of the corolla. They are usually hairless but rarely somewhat hairy below. Fruit are capsules.

Its fruiting spikes contain thousands of minute seeds.

Identification

Ivy broomrape closely resembles the more commonly distributed '' O. minor'' and both are able to parasitize members of the ivy family. ''O. hederae'' is primarily differentiated by its characteristically distally pinched corollas, the flowers extending over most of the stem, the long, acuminate floral bracts, and its large terminal 'bud' of unopened flowers that give the spike a pointed top. The stigma on ''O. hederae'' is usually yellow and the corolla is curved downwards and cream-colored.

Ecology

Ivy broomrape primarily propagates by seeds which are dispersed by wind, but is also able to regenerate from small fragments of roots that remain in the soil. Many broomrape seeds show considerable abilities to remain dormant but viable for many years.

When germination occurs, the embryo of the seed sends out a thin thread-like filament that spirals away from the embryo and into the surround soils until it makes contacts with ivy roots. The filament then penetrates xylem tissues which allows it to receive water, nutrients, and carbohydrates from its ivy host. The connection made with the host can be so complete that its nearly impossible to tell with certainty where the epidermis of the host ends and where that of the parasite begins. In order for a seed to survive, this connection must occur within a few days of germination. Only once enough energy has been garnered will the plant send up a flower stock and be visible above ground.

Host specificity

Ivy broomrape is an obligate parasite of ivy (''Hedera'') plants, primarily affecting ''English ivy'', but, rarely, other species as well. It contains no chlorophyll of its own and seed germination is dependent on strigolactone root exudates of the host. Unlike more weedy species of broomrape like common broomrape, ''O. hederae'' exhibits very high host specificity based on germination measurements in response to kinds of strigolactone typical of various possible host plants.

It is one of two parasitic plants associated with common ivy; the other being '' Osyris alba''. However, osyris has a very wide host range while ''O. hederaes range is extremely narrow.

Seasonality

Pollen units are medium sized (26-50 μm) spheroidal monads. Flowering can take 2 years after infection to occur. However flowering is influenced by or coordinated with their host. Ivy broomrape sown onto an alien host like ''Tetrapanax'' was shown to flower in a single year. In Mediterranean climates it flowers from late April to mid July. In the UK, flowers are generally observed in June and July, June–August in the Netherlands, and in Ireland flowering generally occurs March–July. Flowering can vary widely and some sources even cite its flowering months to range from April to October.

Distribution

Its native distribution matches that of its host, ivy, so it is mainly found in central and Northern Europe as well as parts of Asia. In the US, it has been observed in a patch of invasive ivy at the University of California, Berkeley, near the life sciences building.

Phylogeny

''O. hederae'' is usually included in the "Orobanche" section of genus ''Orobanche'', which contains about 120 species not counting ''Phelipanche'' species. Phylogenetic studies suggest the amethyst broomrape ('' O. amethystea'') is its closest relative. ''O. amethystea'' primarily parasitizes field eryngo (''Eryngium campestre'') which is in the order Apiales.

Uses

The Greek physician Dioscorides wrote that the plant, called ''ὀροβάγχη'', can be eaten raw or cooked like asparagus and also stated that cooking the plant with pulses makes the pulses cook faster. While Dioscorides doesn't include medicinal information in his description, Russian and Northern folklore both describe the plant as highly medicinal.

A review of literature of traditional use of ''Orobanche'' shows that while broomrapes were used as food and medicine throughout regions of the world, this usage mainly happened in China and North America. While in Europe, they were primarily used as food items only.

Gallery

File:Achlorophyllous root parasitic plant ivy bromrape (Orobanche hederae Duby).jpg
File:Broomrape, Cricketfield Road, Torquay - geograph.org.uk - 828455.jpg
File:Orobanche hederae inflorescence (15).jpg
File:Orobanche hederae (scott.zona).jpg
Orobanche hederae Buskett Gardens Malta 02.jpg
Orobanche hederae inflorescence (16).jpg
Orobanche hederae inflorescence (85).jpg

References

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hederae
Flora of Europe
Plants described in 1828