Inflorescence cormlets in Watsonia meriana

All corms and cormlets produced by a Watsonia are axillary. Sympodial branching is a diagnostic character of the genus, with the main corm being exhausted by producing an annual flowering stem and one or several new lateral underground corms each subtended by a basal leaf. Additional smaller corms, variously called cormlets, cormils or bulbils are typically produced in the axils of lower cauline leaves in many species including W. aletroides (Burm.f.)Ker Gawl., W. humilis Miller and W. meriana (L.)Miller.

The Watsonia inflorescence is a spike with each solitary, sessile flower subtended by an outer bract and a less robust inner bract. The weedy variety W. meriana var. bulbillifera (J.Mathews & L.Bolus)D.A.Cooke is distinguished by having the lower flowers in its inflorescence replaced by clusters of cormlets. This variety is usually a sterile triploid depending on above-ground cormlets for dispersal, and is known as bulbil watsonia.

However, some genotypes of diploid W. meriana var. meriana can produce small solitary cormlets or cormlet clusters in the inflorescence, at least in cultivation. The extent of cormlet development is variable from one year to another; they are sometimes absent and are never as large or numerous as in var. bulbillifera.

Accession 183. At the right of the picture is a typical solitary cormlet 3mm wide produced in the axil of the reduced leaf subtending an inflorescence branch – but on the outside of that branch. This has been observed on all branches in six out of eight years. To the left is a cluster of six cormlets replacing the lowermost flower on the main axis; this has only been observed once.

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Accession 187. A cluster of three cormlets replacing the lowermost flower of the inflorescence. This has only been observed once in eight years.

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I used to wonder if the cormlet clusters of var. bulbillifera might be homologous to the twelve organs (six tepals, three stamens, three carpels) in a flower. This hypothesis was attractive because, although the number of cormlets in each closely packed cluster is variable, twelve is a typical number. The observations reported here make the hypothesis much less likely. There is a gradient transition from stem cormlets through inflorescence cormlets to clusters. The position of the cormlets in accession 183, axillary to the phyllome subtending an inflorescence branch but abaxial to that branch as if an extra axillary growing point, is rather surprising.

The consistent development of inflorescence cormlet clusters is still the morphological character separating var. bulbillifera from var. meriana. However, the difference should be understood as one of degree rather than a clear dichotomy.

Accession 183 was a gift from Mr Graeme Dallimore who collected it on Mornington Peninsula, Victoria. Accession 187 is said to be Cronin material discarded from Melbourne Botanic Garden in 1995. Both readily produce seed, implying that they are diploids.

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References

Conran, J.G., Wilson, P.A. & Houben, A. (2004). Pollination and ploidy changes in South Australian populations of bulbil watsonia, Watsonia meriana (L.)Miller var. bulbillifera (J.Mathews & L.Bolus)D.A.Cooke (Iridaceae). Herbertia 57: 57-70.

Cooke, D.A. (1998) Bulbil watsonia is a variety of Watsonia meriana (L.)Miller (Iridaceae). J. Adelaide Bot. Gard. 18: 5-7.

Goldblatt, P. & Manning, J.C. (2020) Iridaceae of southern Africa. Strelitzia 42. (South African National Biodiversity Institute: Pretoria).

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