The history of Reseda odorata - can it revert to its wild ancestor?

Reseda odorata L. (sweet mignonette) is often grown as a cottage garden annual for its scent and is cultivated commercially in Europe for the perfume industry.

Its closest wild relative is Reseda phyteuma L., whose native range covers the Mediterranean region, including Algeria, Morocco, Portugal, Spain, southern France, Italy and the Balkans, with climates that match those in the agricultural zones of southern Australia (Carter, 1993). In these countries it is regarded as a minor weed of cleared ground, having low ability to compete with crops. It is now also naturalised in a few vineyards near Clare in South Australia (St John-Sweeting, 1994); this population was at first believed to be R. odorata (Cooke, 1991). This is its only known contemporary occurrence in Australia. Its short life cycle, ability to flower at any time of the year and produce large numbers of seeds (some of which germinate immediately while the others remain dormant) enable it to grow as an opportunist on soil that has been kept bare by cultivation.

The same characteristics also pre-adapted R. phyteuma as a self-seeding garden annual. Abdallah & De Wit (1978) first proposed that R. odorata is a domesticated derivative of R. phyteuma, and suggested that early agriculturists tolerated R. phyteuma in their gardens and gradually selected it for more attractive flowers and a stronger fragrance. This domestication process was believed to have occurred around Egypt and Libya, as plants of the Reseda odorata/phyteuma complex have been cultivated in Egyptian flower gardens since the Roman period. However, there is no evidence of their use in earlier times: no plant resembling a Reseda appears in the thorough reviews of the archaeological evidence for ancient Egyptian flower gardening by Manniche (1989) or Kantor (1999). By the first century CE they were widely grown for their perfume in the Roman and Hellenistic cultures around the Mediterranean. The plant phyteuma mentioned by Dioscorides as an aphrodisiac is likely to be Reseda phyteuma, which has a faint musky scent reminiscent of the mammalian pheromone androsterone. Pliny described a plant widely grown for its aphrodisiac scent which was also used in treating bruises - for this reason he gave it the latin name reseda, meaning a healer or restorer.

Reseda odorata was introduced to England around 1750 (Miller, 1754), and within a decade had become so popular that Miller (1759) reported that unscrupulous seedsmen were supplying R. phyteuma as a substitute. However, he also made the interesting observation that some gardeners believed their plants had degenerated into a scentless form over several generations.

It appears that R. odorata can revert to a form with the weak musky scent of R. phyteuma unless the strong scent character is maintained by deliberate selection. In Australia, where it had been introduced by 1837 at the latest (Stephens, 1839), it has often persisted in gardens by self-seeding. Seed catalogues of the 1930s mention named cultivars such as 'Machet', 'Golden Machet', 'Machet Improved', 'Red Giant', 'White Pearl', 'Goliath' and 'Incomparable'; these had single or double flowers ranging from white through yellow to deep red (Brunning, 1934). But all of them were open-pollinated lines and commercial seed growers did not select to maintain the scent quality. As a result, these Australian garden strains had become scentless by the late 20th century when scented cultivars were re-introduced from New Zealand (Nottle, 1992).

In Australia, feral R. odorata can only be found close to former plantings in gardens or cemeteries. They differ from the cultivated strains in their weak scent, gracile and often decumbent habit, and sometimes in smaller anthers. In these characters they resemble R. phyteuma.

In their revision of Reseda, Abdallah & De Wit (1978) state that R. odorata is known only as a cultivated plant or a garden escape; there are no truly wild populations. The known occurrences in Libya are more likely to be garden escapes than a "natural" population that gave rise to the cultivated plant. Like the garden escapes in Australia, they are small decumbent plants with weakly scented flowers. Another a wild population in the Deccan of India that has been given the name of R. odorata var. neilgherrensis differs in having ascending stems, yellowish petals and a longer central lobe on the upper petal. As this is remote from the natural range of R. phyteuma and the supposed origin of R. odorata, and also resembles the feral R. odorata in Australia, it is almost certainly derived from a garden escape.

For centuries, it was taken for granted that domesticated plants and animals had a tendency to revert to their ancestral types when turned wild and allowed to breed freely; Wallace (1859) even called this reversion a 'law' in contrasting the behaviour of anthropogenic and natural varieties. Modern knowledge of genetics makes us sceptical of such vague generalisations - but considering that:

• alleles common in wild populations are usually dominant over their rarer mutant homologues
• biotypes established in wild populations tend to resist change because they are buffered by many genes
• natural selection in conditions similar to the native habitat will strongly favour the wild biotypes over those produced by artificial selection

The origin of the isolated infestations of Reseda phyteuma at Clare has been a mystery. The hypothesis of an actual incursion of a weed from overseas raises the possibility of eradication, but also raises the question of why the incursion occurred at that site. The alternative hypothesis of a garden escape reverting to its wild ancestor would dismiss both of these concerns.

References

Abdallah, M.S. & De Wit, H.C.D. (1978) The Resedaceae - A taxonomical revision of the family. Meded. Landbouwhogesch. Wageningen 14: 99-416.

Brunning, L.H. (1934) The Australian Gardener. 23rd edn (Robertson & Mullen: Melbourne).

Carter, R.J. (1993) Rampion mignonette and its co-ordinated control. Proc. 10th Australian & 14th Asian-Pacific Weed Conf. 1: 505-509.

Cooke, D.A. (1991) New records in the naturalised flora of South Australia IV. South Australian Naturalist 65: 60-66.

Kantor, H.J. (1999) Plant Ornament in the Ancient Near East. (Oriental Institute, University of Chicago).

Manniche, L. (1989) An Ancient Egyptian Herbal. (British Museum Publications: London).

Miller, P. (1754) The Gardeners Dictionary. 4th edn (London).

Miller, P. (1759) The Gardeners Dictionary. 7th edn (London).

Nottle, T. (1992) Old-Fashioned Gardens. (Kangaroo Press: Kenthurst).

Stephens, J. (1839) The Land of Promise. (Smith, Elder: London).

St.John-Sweeting, R. (1994) Rampion mignonette spreading in the Clare Valley. The Australian Grapegrower and Winemaker June 1994: 36-38.

Wallace, A.R. (1859) On the tendency of varieties to depart indefinitely from the original type. J. Linn. Soc. 3: 45-49.

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