Flower colour in Chasmanthe floribunda (Iridaceae: Ixieae)
The South African cornflag, piempiempie or Aunt Eliza, Chasmanthe floribunda (Salisb.)N.E.Br., is common in southern Australia as a no-maintenance garden plant and also as a weed of native vegetation. The wild-type has a purple inflorescence axis, orange-red perianth with some yellow on the perianth tube, and purple anthers.
About 30% of the plants in cultivation represent a variant with a green inflorescence axis, entirely yellow perianth and yellow anthers. Apart from its lack of red pigment, the yellow variant is indistinguishable from the wild-type in its morphology. It was treated as C. floribunda var. duckittii by Bolus (1933), and has also been called by the informal name 'Antholyza lutea' in horticultural publications (eg. Shum, 1939). No plants with intermediate flower colour have been observed, although the species regenerates freely from self-sown seed.
De Vos (1985) suggested that the "lower portion of the perianth tube", ie the hypanthium, was shorter in var. duckittii but did not cite any measurements. Flowers of plants in suburban Adelaide gardens and roadside populations in the Adelaide hills had hypanthium lengths of 9-11 mm, irrespective of flower colour.
Experimental crosses
The red pigment is also absent from the plumule of the seedling and etiolated shoots emerging from the corms; they are cream in this variant but reddish-tinted in wild-type plants. This suggested the simple experiment of crossing red- and yellow-flowered plants and scoring their progeny at germination for pigment.
Cross pollination was carried out between a 'red' and a 'yellow' plant; reciprocal crosses were made to check for any apomixis or accidental self-pollination.
Flowers of a 'red' were pollinated with pollen from a 'yellow'
Flowers of a 'yellow' were pollinated with pollen from a 'red'
These results are in accord with a 1:1 ratio (Chi-square 0.281, yielding a probability of 0.595). Four randomly selected plants from each of the 'red' and 'yellow' seedlings were grown through to flowering; all four scored as red produced wild-type red flowers, all those scored as yellow produced pure yellow. No intermediates between red and yellow were produced in the experiment. The simplest hypothesis is that a single gene is involved, with red fully dominant over yellow; the red plant used in the cross would therefore have been a heterozygote to give the observed 1:1 ratio in the F1.
Selfing of the two plants used in the experiment was then attempted; this failed, due to self-incompatablility (common in the Iridaceae).
Petals of both flower types were then examined under a light microscope at 200X. The red anthocyanin pigment was seen to be dispersed through the cell sap in the red flowers, but could not be found in the yellow flowers; the yellow pigment (presumably a carotenoid) was concentrated in chromoplasts in both red and yellow flowers.
Conclusion
Yellow-flowered C. floribunda plants do not warrant formal taxonomic recognition. They are acyanic variants, analogous to the white-flowered 'albinos' found in many garden ornamentals, which are no longer formally recognised except at the level of cultivars. To borrow a term from aviculture, they may be characterised as a lutino variant, in which pigments other than yellow are absent.
References
Bolus, L. (1933) Plants - new or noteworthy. South African Gardener 23: 46-47.
de Vos, M.P. (1985) Revision of the South African genus Chasmanthe (Iridaceae). South African J. Bot. 51: 253-261.
Shum, W.A. ed. (1939) Australian Gardening of Today. (Sun News-Pictorial: Melbourne).
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