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Issue 17

The Native Citrus Tag

Anthony Hele, Industry Development Consultant - Native Foods

There has been discussion of late in Bushfoods magazine and elsewhere about some presumed confusion in citrus nomenclature or classification arising from the release of the CSIRO-bred native citrus hybrids Australian Blood Lime PBR and Australian Sunrise Lime PBR.

The botanic taxonomy and horticultural nomenclature of citrus generally is complex, but not necessarily confusing to those in the industry. Firstly it should be remembered that citrus classification schemes may be either botanical (and aim for scientific accuracy) or horticultural (and aim for commercial utility). While there are several classification schemes around, the industry basically divides commercial ly important citrus into eight common horticultural and botanical groupings:

Sweet Orange (Citrus sinensis) Mandarin (Citrus reticulate) Grapefruit (Citrus paradisi) Pummelo (Citrus grandis) Lemon (Citrus limon)

Sour Lime (Citrus aurantifolia) Citron (Citrus medica)

Sour Orange (Citrus aurantium) While the above scheme seems relatively straightforward, the complexity in citrus naming and classification and differences in botanical and horticultural des Icynations largely arise from the plants' ability to readily hybridise. Botanical classifications attempt to recognise these hybrids by employing terms such as tangor (mandarin-orange hybrid),

lemonime (lemon-lime hybrid), lemonange (lemon-orange hybrid) and lemandarin (lemon-mandarin hybrid). However these terms are not generally employed as horticultural or commercial designations.

The most common and notable examples of how this factor influences citrus tags are found in

the mandarin group, where varieties such as Ellendale and Murcott are actually tangors and Fairchild, Nova, Osceola and Robinson are hybrids between mandarins and tangelos (i.e. hybrids between mandarin and grapefruit). In each of these cases these cultivars are generally known and traded as mandarins, despite their hybrid origin and botanical designations.

Some exceptions do exist however, several mandarin-grapefruit hybrids, such as Minneola and Seminole, are both botanically and horticulturally known as tangelos. In this case marketing considerations, rather than any concern for botanical accuracy, has been the likely motivation for the common adoption of this name.

Even the Meyer lemon, well known to many home gardeners, is not a true lemon, most likely being a hybrid between lemon and either an orange or a mandarin. It is never sold as a 'Meyer lemonange' or 'Meyer lemandarin'. An even more curious situation occurs in the US, where a particular tangor cultivar is known and marketed as Temple orange when grown in Florida and as Royal mandarin when grown in California.

If we go back further and look at the basic groups themselves it becomes even more complex. For example the sweet orange is probably the result of a natural pummelo-mandarin cross and the grapefruit from a cross between pummelo and sweet orange. The lemon is a more complicated hybrid, possibly involving the lime, citron and perhaps pummelo. Even the most pedantic is unlikely to argue that, to avoid confusion and misrepresentation, oranges should really be known as pummelarins and lemons as limronelos.

So how does this potential complexity impact on citrus science, culture and trade? And how does it effect the likely horticultural classification of Australian native citrus species, cultivars and hybrids?

In terms of horticultural classifications the key lies in the common sense approach used by the world citrus industry. As Robert

Some of the citrus discussed

Hodgson (former Professor of Subtropical Horticulture at the University of California, Los Angeles) explains in his chapter on Horticultural Varieties of Citrus in Volume 1 of 'The Citrus Industry' (The Bible) - 'the horticultural classification employed is ... both arbitrary and empirical... Since the classification is based primarily on resemblance, it has been best to place known and presumed hybrid varieties in the groups they most resemble, irrespective of parentage, known or presumed'.

This rule - if it most closely resembles a mandarin, call it a mandarin - is a profoundly logical approach to dealing with what could be overwhelming complexity. Moreover, within his classification he does explain the parentage of each cultivar, so ultimately there can be no confusion or misrepresentation, and more complex botanical designations and classifications can still be employed when the context is appropriate.

Currently there are, as far as I am aware, only four cultivars and hybrids of Australian native citrus commercially available (although doubtless there are others waiting in the wings). Two are pure species cultivars, namely Rainforest Pear] PBR (Citrus australasica var. sanguinea) and the Australian Outback LimePBR (Citrus glauca). The other two are hybrids and are known as the Australian Blood Lime PBR - a natural hybrid of the sour-fruited mandarin-like Rangpur, (Citrus limonia) and Citrus australasica.var sanguinea; and the Australian Sunrise Lime PBR - an open-pollinated seedling selection of the faustrimedin. The faustrimedin is a hybrid of Citrus australasica and calamondin - itself a hybrid of mandarin and cumquat.

It seems a totally logical and acceptable practice to apply Hodgson's maxim in this situation and at this stage to horticulturally classify all these cultivars under the heading of `Australian native citrus', and as long as an explanation of the parentage of each variety is readily available there can be no question of confusion or misrepresentation.

Further, 'foreign' citrus species have been present in Australia for more than 200 years and readily hybridise with native species to produce offspring that often strongly resemble their native parent. Attempting a practical horticultural classification based on some concept of 'genetic purity' seems to me to open up an unnecessary can of worms and raises the spectre of DNA testing for every new 'native' variety offered for sale.

However, in practice the real bottom line is this - it is the citrus industry and market that will ultimately decide whether 'Australian native citrus' stands as a horticulturally and commercially distinct group and what species, cultivars and hybrids are included. Experience shows that botanical designations and concepts of 'genetic purity' are unlikely to be significant factors in this decision.

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