The other day, I found myself standing under a Broussonetia tree in the Cambridge University Botanic Garden (so happily now reopened, though you do have to book), and was reminded of my oft-repeated note to self to find out more about this paper mulberry, at one time so important to the civilisations of the Far East and the Pacific, but now in many places an invasive ‘weed’, with pollen so toxic that it is a severe danger to those with allergies.

Broussonetia kazinoki, a Champion Tree in @CUBotanicGarden

In fact, the tree in question was Broussonetia kazinoki, the Kozo paper mulberry, from Japan, rather than the more famous Broussonetia papyrifera, widespread across east Asia. To get the taxonomy out of the way: if I understand it correctly, the true paper mulberry was named Morus (i.e. mulberry) papyrifera by Linnaeus, but got its current binomial from Étienne Pierre Ventenat (1757–1808), who started off as a librarian but was so impressed by the botanic gardens of Great Britain that on his return to France he studied for several years under L’Heritier. Rather touchingly, it is claimed that he was so dismayed by the mediocrity of his first publication, Principes de botanique, expliqués au Lycée républicain par Ventenat (1794) that he tried to buy up all the copies and destroy them.

It was in his next book, a three-volume translation out of Latin into French of Antoine Laurent de Jussieu’s Genera plantarum (1789), with additions of his own on the properties and uses of plants, entitled Tableau du règne végétal selon la méthode de Jussieu (1798), that he defined Broussonetia papyrifera. In his observations on the plant, he noted that, as Citizens L’Heritier (who first used the name Broussonetia to honour Pierre Marie Auguste Broussonet (1761–1807, a Montpellier naturalist who was big on fish as well as plants) and Lamarck had not yet published a description of this species, he himself would do so from garden study, as the tree was cultivated with success in several gardens in the environs of Paris. He also stated that those wishing to know how paper is made from the plant should consult the works of Kaempfer and Thunberg.

Pierre Marie Auguste Broussonet (1761–1807)

Pausing to note only that Ventenat wrote the text for Le Jardin de la Malmaison, commissioned by ‘Madame Bonaparte’ (later the Empress Joséphine), and published in 1803, which is rather more famous for its illustrations by Redouté, we can return to the trees.

The title page of the ‘Malmaison’ book

I have two photographs taken in Italy in former years, and both were of the bark – one because I was writing about bark, and the other because I wanted to show the deep incisions made by ivy into the trunk – so I am relying on external sources for most of the pictures: the Ebben Tree Nursery in the Netherlands has a good display.

This B. papyrifera is the the Botanic Garden at Florence …

… and this trunk, in Venice, is scarred by generations of ivy.

Like the dreaded Gingko biloba, the species has male and female plants: the one in the Botanics is evidently female (and I’m sorry to have missed the rather attractive flowers). The flowers of B. papyrifera (which I missed in Italy this year) are spectacular, and the catkins of the male plants furry and substantial.

The flowers of Broussonetia kazinoki.

As the fruits of B. Papyrifera form, the red remains of the flowers drop off. (Credit: Chiltern Seeds)

The male catkins, of which the pollen is toxic.

(This article, which describes the tree’s invasive tendencies in Pakistan, notes that a scheme to ‘green’ Islamabad quickly, which involved spraying seeds of B. papyrifera from a helicopter over forty years ago, has resulted in endangering many native species by overshadowing and crowding out; and that ‘trees bearing staminate catkins should be removed from areas where invasion appears imminent and a major cause of asthma and related allergies due to its pollen’.)

In Europe, B. papyrifera (and other species) are grown for their decorative features, the first seeds in Britain having been obtained by Peter Collinson (more famous for his cooperation with John Bartram in introducing north American plants) in 1751. But, as Engelbert Kaempfer (1651–1716) pointed out in his Amoenitatum exoticarum politico-physico-medicarum Fasciculi V (1712), in Japan and China it had been for centuries a most important part of the agricultural economy, because it could be used (though heaven knows who first worked this out) to make paper.

The opening of Kaempfer’s description of Japanese paper-making, with a historical overview of the writing surfaces used in the ancient Near East.

Kaempfer wrote in Latin; having struggled through his explanation, I was relieved to see that my understanding of the process more or less matched this film of modern, mostly automated, manufacture (which must win the prize for the most dreary-voiced narrative ever) and another piece describing how you can try it at home. (Thunberg’s account (in his Flora Japonica of 1784) is more or less identical to that of Kaempfer, to whose work he refers.)

Basically and briefly, in December (in Japan), branches are cut from the trees, cut into suitable lengths, and then boiled and beaten (and bleached) in stages so that the outer bark can be peeled off and the inner bark can be separated from the core wood (the more core wood left in, the cruder the paper). Eventually, the resultant pulpy liquid is poured into paper-making frames, the water falls through the mesh and the soft interlinked fibres of the inner bark dry out as paper. (In the film, the paper is also shown being produced as a reel.) Among other uses, very light weights of this paper are employed as a strengthening material to repair rare books and manuscripts. (Some samples can be seen on the website of the inestimable Shepherds Bookbinders.)

A nineteenth-century Japanese print on mulberry paper.

While B. papyrifera was used in Japan and China for paper, in the Pacific islands, the same trees provided the raw material for barkcloth, and it is claimed that the presence of the trees in the Pacific is an argument for the theory that the islands were originally populated from the south China coast c. 3000­­–1500 BCE, stone beaters for breaking down the fibres of the branches being one of the tools found across the area from the Neolithic period. The cloth is called tapa in Tahiti, from where Captain Cook (or was in it fact Joseph Banks?) is believed to have brought the first examples back to Europe – some of them are now in the Museum of Archaeology and Anthropology in Cambridge, and were featured in the Oceania exhibition in the Royal Academy in 2018.

In A Journal of a Voyage round the World, in His Majesty’s Ship Endeavour, of which the authorship is uncertain, but which must have been written by a crew member, possibly Banks’s draftsman, Sydney Parkinson, the process of making the cloth by women is described: ‘After the bark has been soaked in water for a few days, they lay it upon a flat piece of timber and beat it out as they think proper with a kind of mallet of an oblong square, each side of which is cut into small grooves of four different sizes: they begin with that side where there are the largest and end with the finest, which leaving longitudinal stripes upon the cloth makes it resemble paper.’

A piece of paper mulberry barkcloth from Samoa, acquired in 1887. (Credit: the British Museum)

A barkcloth beater, collected in Tahiti, 1854. (Credit: the National Museum of Australia)

There is a useful series of videos from Auckland, New Zealand here, though these take the view that cloth-making began in Papua New Guinea and spread across the Pacific from there – the bark of breadfruit (Artocarpus altilis), which originated in that region, can be used in the same way as that of the paper mulberry.

It is dismaying that in some parts of the world, Broussonetia papyrifera is an invasive weed – from Pakistan to Argentina to Uganda, it is driving out, overshadowing or undermining the native flora – but cheering to think that the traditions of using the tree for paper-making and cloth production continue today, after at least one thousand years for the former, and many thousands for the latter.

Caroline