Purple Broomrape, Orobanche purpurea

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Yarrow Broomrape

Purple Broomrape at Beeston Regis

Sometimes, in the middle of winter, the only escape is to look forward to long summer days full of plants.

In the middle of June last year we took the train to Sheringham on the North Norfolk coast and walked to Cromer. Descending Beeston Bump we were rewarded with a new species of plant, Purple Broomrape, Orobanche purpurea. This is a very handsome beast, with dark purple flowers on a purplish brown stem. It looked very striking against the greenery of other plants, including grasses, horsetails (Equisetum), Kidney Vetch (Anthyllis vulneraria) and Yarrow.

The Yarrow (Achillea millefolium) was the reason that the Purple Broomrape was growing there. Also known as Yarrow Broomrape, Orobanche purpurea is a parasite on Yarrow.

Mistletoe, which I wrote about in December, is a hemi-parasite: although it takes some of its nutrients from its host, it possesses chlorophyll and makes its own sugars. Broomrapes are holo-parasites: they are utterly dependent on their hosts for food.

Purple Broomrape has no leaves and does not photosynthesise. It has an underground tuber and attaches to its host underground by means of haustoria. It is a member of family Orobanchaceae, which contains about 90 genera and 2000 species of herbs and shrubs distributed throughout most of the world. All, except for the genera Lindenbergia and Rehmannia, are hemi- or holo-parasites on the roots of other plants. See Wildflowers-and-Weeds.com for some lovely photographs of American members of the family.

Fourteen species of Orobanche have been recorded in the British Isles. Although “A Flora of Norfolk” (Gillian Beckett, Alec Bull & Robin Stevenson, 1999) lists five species of Orobanche in Norfolk, Hemp Broomrape (O. ramosa) was only recorded in 1880 and Greater Broomrape (O. rapum-genistae) was last seen in the county in 1986. This leaves three species: Purple Broomrape, Common Broomrape (O. minor) and Tall or Knapweed Broomrape (O. elatior). I have seen the latter once, on Marriott’s Way near Norwich, though it is more common in West Norfolk. In contrast, Common Broomrape is much more widespread and is found with a variety of host plants, including clovers (Trifolium) and various members of the Asteraceae (daisy family). Several years ago it was abundant amongst shrubs by a car park in Westwick Street in Norwich and we found it growing amongst Hyssop in Grapes Hill Community Garden in 2012.

Purple Broomrape is much rarer than its common and widespread host plant, Yarrow.  Nationally, Purple Broomrape is a plant of clifftop grasslands and, sometimes, disturbed places, on dry, slightly alkaline soils. It has the habit of disappearing for several years and then reappearing, which suggests that it can persist without flowering for many years, or has long-lived seeds. In the UK it is classed as vulnerable (see map and list of sites), but North Norfolk is one of its hotspots, along with the Isle of Wight and the Channel Islands. It can also be found on sand dunes in the Netherlands and its natural range is across Europe, as far south as Spain, Portugal and Greece, east to central Russia, the Caucasus, Asia Minor, Pakistan and India and north to Sweden. It has also been reported from Canary Islands, Morocco, and North America. (In Iran it has been recorded on a close relative of Yarrow, Achillea wilhelmsii.) However, it is endangered in much of its range as grasslands are destroyed and agriculture intensifies. The paper by Renata Piwowarczyk, “Orobanche purpurea (Orobanchaceae) in Poland: current distribution, taxonomy, plant communities, and preferred hosts” (Biodiv. Res. Conserv. 26: 73-81, 2012) gives a good, if sobering, summary.

At the time of writing, the Plants for a Future website lists ten species of Orobanche, but not O. purpurea and given its rarity it would be criminal (literally) to harvest it. Our Orobanche minor has no known edible uses, but Orobanche ammophyla is used as a food and medicine in China (mind you, so are tigers) and other edible and medicinal species include the North American Orobanche fasciculata.

If you want to see Purple Broomrape on Beeston Bump, you can follow Walk 8 in this walk leaflet. Stick to the paths and go in June or July. Last year there was lots of Purple Broomrape, but be aware that the number of flowers varies from year to year.

Mistletoe, Viscum album

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“Mistletoe,” said Luna dreamily, pointing at a large clump of white berries placed almost over Harry’s head. He jumped out from under it. “Good thinking,” said Luna seriously. “It’s often infested with nargles.” – J. K. Rowling – ‘Harry Potter and the Order of the Phoenix’.

Mistletoe

Mistletoe, Viscum album, growing in an apple tree.

It’s less than a week until Christmas, and it seems like a good idea – or at least a topical one – to write about Mistletoe, Viscum album.

Mistletoe is associated with the Winter Solstice and midwinter celebrations, specifically, the tradition of kissing under the mistletoe. Mistletoe plants are cut from trees, brought indoors and hung up. According to the WhyChristmas.com website, the original custom involved picking a berry from the sprig of Mistletoe and then kissing, until all the berries had gone. Nowadays the berries are left on the sprig, which is much more economical.

In continental Europe Mistletoe was regarded as a plant of peace and luck and in France it was often given as a Porte Bonheur (a gift for luck), at New Year, rather than Christmas.

The association between Mistletoe and kissing seems to date back to ancient beliefs about fertility, which are older than the Christian church. Mistletoe is an evergreen plant that grows mainly on deciduous host trees and provides a dramatic flush of greenery in the middle of winter amongst leafless boughs. Mistletoe’s shape may also be significant: its branches fork, it has paired leaves and its berries are full of sticky white juice – all suggestive of sexual organs in both shape and content. There are also links to the Ancient Greek story of Aeneas and the Golden Bough and the Norse legend of Baldur.

The kissing tradition may be in decline, which is a shame. A survey by a major British supermarket found that 71% of respondents under 35 had never been kissed under mistletoe, and only 14% of those surveyed had kissed under the mistletoe in the last year. But enough of kissing for now: Mistletoe is fascinating in lots of different ways.

Mistletoe, Viscum album, is a member of the Sandalwood Family, the Santalaceae. (It was previously considered to be in the family Viscaceae,  the Mistletoes.) It is a hemi-parasite. It needs to grow on a host plant for support, water and nutrients, but it has green leaves and manufactures its own sugars by photosynthesis. In the UK Mistletoe (subspecies album) can be found growing on several different tree species, including Poplars, Limes, Apple and Hawthorn. Mistletoe rarely grows on Oak, in spite of legends of druids with golden sickles gathering it from sacred oak groves, a story that seems to have originated with Pliny the Elder. In continental Europe, there are two more subspecies of Viscum album: austriacum grows on pine trees and abietis on fir trees.

Mistletoe is dioecious, with separate male and female plants. The males flower between February and April and produce clusters of insignificant flowers with four tiny petals in the fork between two branching stems. Female plants produce the familiar white berries in November and December.

Mistletoe berries are very sticky and are spread from tree to tree by birds, which eat the berries and remove the sticky seed by wiping their beaks against the bark of a tree. The scientific name of the Mistle Thrush, Turdus viscivorus, means “thrush that eats mistletoe”. Fieldfares also like the berries, but Blackcaps appear to be best at spreading them about. At one time Blackcaps were only found as summer migrants in Britain, but in recent decades continental birds spend the winter here, at the time that Mistletoe has its berries. As a result, the plant may be on the increase in the East of England. It seems to be particularly common in Common Lime and poplar trees in South Norfolk and we have some plants here in Norwich. (One can be seen when heading eastwards by train out of Norwich station; another is high on a tree on The Avenues, only hundreds of yards from my house.)

Once a Mistletoe berry has stuck to a suitable host tree, it forms a swollen holdfast. A stem and root-like haustorium grow out from the holdfast and the haustorium penetrates the host and starts to take water and minerals from its vascular tissue . Mistletoes are very highly adapted to their hemi-parasitic lifestyle. It is claimed that the germinating seeds of one species, Loranthus globosus,can ‘walk’ along a tree branch by flipping end over end until they become successfully wedged into the bark.

Mistletoe’s former stronghold was in apple growing areas along the Welsh boder, such as Herefordshire, though it has declined with the loss of our traditional orchards. Mistletoe is traditionally harvested and sold as a crop at Christmas time, and this harvest is beneficial because it stops the plant from becoming too vigorous. If left unchecked, Mistletoe reduces the productivity of its host tree, can cause stress in dry weather and may ultimately kill its host.

Mistletoe is locally common in the UK: Here are maps of Mistletoe distribution in the UK and worldwide. (The plant has been introduced to other parts of the world, including the United States.)

Worldwide, there are over a thousand species of Mistletoe and in Europe there are three more species of Mistletoe, as well as our Viscum album. The Red-berried Mistletoe, Viscum cruciatum, is found in southern Spain and grows on Olive trees, the Yellow-berried Mistletoe, Loranthus europeaus, is deciduous and grows on Oak trees and the tiny Dwarf (or Juniper) Mistletoe, Arceuthobium oxycedri, grows on Juniper. There are several North American and African species. A spectacular species from Western Australia, Nuytsia floribunda, is known locally as the Christmas Tree because it flowers in December. It grows as a free-standing tree but is nevertheless a hemi-parasite, with roots that reach out and take nutrients from nearby plants. When it grows near houses its roots will even latch onto underground electric cables and small irrigation pipes, causing damage (and even a short-circuit).

Mistletoe is poisonous to humans, though its toxicity is described as ‘slight‘ and the Plants For A Future website says that the ripe berries are edible (with caution). The active ingredients are viscotoxins and mistletoe lectins. Mistletoe poisoning can cause pale lips, inflamed eyes, dilated pupils, slow pulse, hallucinations and coma and may result in hepatitis. Mistletoe extracts have been used to treat stomach, lung and ovarian cancers and they are now marketed in Germany as ‘Iscador’ and ‘Helixor’, although their exact mechanism of action is still under investigation. Mistletoe has also been used to treat epilepsy, ulcers, high blood pressure and rheumatism and appears to have antiseptic, antispasmodic, astringent, digestive and diuretic properties.

If you want to grow your own Mistletoe, there are some great instructions and photos here.

The Mistletoe Pages website has lots and lots more information, plus free information sheets to download, posters and even a book about Mistletoe.

Oca, Oxalis tuberosa

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Oca tubers

A bucket full of Oca tubers

Yesterday I lifted my crop of Oca tubers from the allotment: a good harvest of tubers, nearly a bucket full, weighing a stone (14lb or 6.35kg), from twelve plants.

I started off with just five tubers in spring 2014. I was sent these because I was taking part in a Garden Organic Members’ Experiment, a trial of growing Oca in this country. This time last year I harvested about 1lb (2.1kg) of tubers and I ate some of these and saved the rest to start off this year’s plants. I plan to do the same thing with this year’s crop and gradually increase the amount of Oca I grow.

Oca is Oxalis tuberosa, sometimes known as the New Zealand Yam. (It was introduced into New Zealand in the 1860s.) It is a member of the Wood Sorrel family, the Oxalidaceae. It comes from the central and southern Andes, from Venezuela south to Argentina, where it is grown for its root tubers. In Peru and Bolivia, where it thought the plant was domesticated, it is the second most widely grown root crop after the potato. Its development as a food crop may predate the Inca empire.

Oca is a perennial plant with leaves like a bigger version of its relative Wood Sorrel, Oxalis acetosella, and knobbly root tubers which come in a variety of colours: white, cream, yellow, purple, pink, orange and red, in a varety of patterns and combinations. The tubers vary in the amounts of oxalic acid they contain, and some varieties need to be soaked and/or left out in sunlight before they are edible. My Oca tubers are pink and have a slight acid tang which fades when they are cooked.

Oca can be grown in the UK, where it prefers well drained or loamy soils. The plant is adapted to the short day length of the tropics and needs a day length of twelve hours or less to form its tubers. This means that tubers only start to form in September and a couple of months need to elapse before there is a crop worth harvesting. The first sharp frost will kill off the leaves and then the tubers will continue to grow for a couple of weeks afterwards. I accidentally left a few small tubers in the ground last year and each one produced a respectably sized plant the next year, so it should be possible to keep tubers in the ground over winter, at least in sandy soils. You can cover the plants with fleece or even their own frosted foliage, to protect the tubers.

I start my tubers off in small pots in peat free compost and then plant them out about a foot (30cm) apart in early June after the first frosts. Growth is slow to start with and until August the plants form discrete, round clumps. Later on they start to spread out across the soil. Some varieties have pretty yellow flowers but my variety hasn’t flowered. If it is very dry in August and September, it is a good idea to water the plants.

Oca

Oca (left), early August 2015

As tuber growth doesn’t start until late summer it should be possible to plant Oca as late as early August, perhaps after harvesting an earlier crop such as garlic, or interplanting with other crops. The Down The Plot and Growing Oca websites have some good suggestions for timing when to plant. The Growing Oca website also has some tips for increasing the yield. Thompson and Morgan suggest that yields of 1.6lb (0.75kg) per plant may be possible in a good year in the UK.

Unlike potatoes, I don’t bother earthing up my Oca plants. The tubers are shaped rather like “Pink Fir Apple” potatoes but they are not susceptible to potato blight. The leaves are good at suppressing weeds as well. Although the tubers are smaller than potatoes, they have a waxy skin and are easy to clean and I never bother to peel them.

I try to lift my entire crop of Oca and store the tubers in a frost free shed. Potato tubers go green in light and produce the poisonous glycoalkaloid solanine but Oca tubers can be stored in the light. They will start to produce sprouts in the spring, but more slowly than potatoes. They will gradually dry out during the winter, but only very slowly in a cool place.

Oca

Oca plant, lifted, November 2015

Update 6th December 2015: This year, as an experiment, a Canadian friend harvested her Oca plants in mid-November. Rather than immediately putting the tops on the compost heap, she left the smaller tubers attached and hung them up in her garage for three weeks. At the end of this time even the tiniest of tubers had grown in size as they absorbed nutrients from the dying foliage. If you have space, especially if growth is stopped by an early frost, this is well worth a try.

Cooking and Eating

Oca tubers have an excellent flavour. They can be eaten raw, when they have a zingy, slightly acid taste. (Leaving them in sunlight for a few days will make them sweeter.) They can be cut into small pieces and boiled for five to ten minutes, parboiled and mashed or roasted in the oven with olive or sunflower oil. The acidity fades when tubers are cooked: boiled tubers taste like waxy potatoes with a hint of lemon and roasted tubers are like a flavoursome roast potato. Oca is good roasted with other vegetables.

I can recommend Oca Salad with Capers and Cornichons and Warm Oca Salad but I haven’t tried Oca Homity Pie yet. Last night I cooked Hugh Fearnley-Whittingstall’s vegeree recipe and substituted the courgettes (now out of season) for Oca. Coated with spices, the tubers combined well with roasted aubergine and red onion.

Oca tubers contain significant amounts of Vitamin C, zinc and vitamin B12 and some varieties are also high in iron. They are a low calorie food too – 100 grammes of potatoes contain about 75kcal but the equivalent weight of Oca contains around 30kcal. Yet more good news is that although they resemble small Jerusalem artichokes, Oca’s storage carbohydrate is starch rather than the inulin found in Jerusalem artichokes, so Oca does not have the same gaseous side effects when eaten.

The leaves and young shoots can be eaten as a tangy green vegetable, though not too frequently because of the oxalic acid they contain. The flowers are also edible and look very pretty in salads. Mature stems can be used like rhubarb.

Further Reading and Growing

If you want to read more, I suggest you look at the Oca Links page of the Growing Oca website. You may also be interested in the Guild of Oca Breeders (GOB), who are trying to breed day neutral varieties of Oca, which will produce tubers much earlier in the year. The first potatoes were late cropping short day plants but intensive breeding has produced potato varieties that crop as early as mid summer – it should be possible to do the same with Oca.

If you live in the United States or Canada, the Cultivariable website offers several varieties of Oca.In the UK, The Real Seed Catalogue sometimes sells Oca, as well as other unusual tubers such as Yacon. Thompson and Morgan sell Oca tubers that look like the variety I’m growing. Although tubers can be expensive, you should only need to buy them once if you grow your own.

The Blooms ‘n’ Food website has some great photos of the different stages of growing Oca.

Oca – Not Okra!

When I say the name people sometimes think I mean Okra, or Ladies’ Fingers, whose slimy seed pods are used in gumbo and many other dishes. This is a very different plant to Oca. Okra, Abelmoschus esculentus, is a member of the Mallow family, the Malvaceae. It is related to Hollyhocks, which I wrote about in my previous blog post.