Flower development and vasculature in Xyris grandis (Xyridaceae, Poales); a case study for examining petal diversity in monocot flowers with a double perianth

Abstract

Floral morphology, anatomy and development are examined in Xyris grandis (Xyridaceae: Poales), with an emphasis on petal and sepal organogenesis and vasculature. Xyris is one of relatively few monocots in which the perianth is differentiated into two distinct whorls (here termed a double perianth). Xyris also possesses highly unusual perianth vasculature, with each petal being supplied by three veins and each sepal by a single vein, compared with the opposite condition in most other angiosperms with a double perianth. However, perianth development in X. grandis shows a pattern that is typical for monocots, with petals not markedly delayed in development. Xyris grandis is also remarkable for its petal aestivation, with each petal surrounding a stamen and two branches of adjacent staminodes, a type that is not reported for other Xyridaceae and may contribute to secondary pollen presentation. The results are discussed in the context of the diversity of a double perianth in monocots, compared with eudicots. Based on current data, our preferred hypothesis is that meristic differences are at least partly responsible for the apparently widespread occurrence of three‐traced petals in monocots. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 170, 93–111.

Floral ontogeny and vasculature in Xyridaceae, with particular reference to staminodes and stylar appendages

“…Our investigation provides the first comparative study of floral ontogeny and vasculature in Abolboda and Orectanthe, complementing previous work that reported an unusual pattern of perianth vasculature in Xyris species (Remizowa et al 2012). We examined different species of Abolboda that either possess or lack staminodes.…”

“…Species of Xyridaceae differ with respect to this character. A PTTT occurs in the style branches of Xyris grandis (Remizowa et al 2012), though it is not evident in the (different) Xyris species described here, which have hollow styles. The styles of both Abolboda and Orectanthe are solid in their upper regions (with a PTTT) but hollow at the style base, as a result of incomplete syncarpy.…”

“…The relatively small flowers of Eriocaulaceae (the sister family to Xyridaceae) lack elaborate vasculature, so that the petals and sepals each receive a single tiny vascular bundle (Stützel 1998;Rosa and Scatena 2007). Remizowa et al (2012) suggested that the trimerous condition that predominates in monocot flowers could allow a broader base for each petal than in pentamerous flowers, perhaps facilitating the occurrence of three and multi-traced petals in some monocots. However, petal primordia in both Xyris and Abolboda are of similar size, despite the difference in vasculature (three bundles in Xyris and many in Abolboda).…”

“…Walker-Larsen and Harder 2000). Sajo et al (1997) and Remizowa et al (2012) reported an unusual pattern of perianth vasculature in Xyris species: each sepal receives a single bundle and each petal receives three bundles, in contrast with many other heterochlamydeous angiosperms, in which the sepals typically receive three bundles each, whereas the petals receive a single major vascular bundle at the base (Eames 1931;Puri 1951;Endress 2001Endress , 2005.…”

“…sterile stamens) because the stamens also typically receive a single vascular bundle; in contrast, sepals are considered to be derived from leaf-like bracts (reviewed by Remizowa et al 2012). The unusual vasculature of Xyris, together with the absence of staminodes and presence of a floral tube in Orectanthe, Aratitiyopea Data from Dahlgren et al (1985), Kral (1998) andCampbell (2005) Fig.…”