Introduction to Expanded Caryophyllales

Abstract

The order Caryophyllales (s.str., also called Centrospermae) has been identified as a natural group by early workers (Braun 1864; Eichler 1876). The main characters used for the recognition of this group include the free-central or basal placentation, the presence of perisperm instead of endosperm as seed storage tissue, and curved embryos (Bittrich 1993). More recent studies have provided further support for the naturalness of this group. Thus, all Caryophyllales families (with the exception of Caryophyllaceae and Molluginaceae) synthesise the unique betalain pigments (for review see Clement et al. 1994) instead of anthocyanins, which are ubiquitous in all remaining seed plants and ferns. Caryophyllales also possess bound ferulic acid in unlignified cell-walls, a characteristic otherwise known only of some monocotyledons (Hartley and Harris 1981). Ultrastructural studies have revealed that Caryophyllales share a unique type of sieve-element plastids (P3; Behnke 1994), in which a peripheral ring of proteinaceous filaments surrounds a protein crystal (sometimes absent) of either globular or angular shape. Based on the data available by then, Cronquist and Thorne (1994) circumscribed the order Caryophyllales to comprise 11 families: Aizoaceae, Amaranthaceae, Basellaceae, Cactaceae, Caryophyllaceae, Chenopodiaceae (including Sarcobataceae and Halophytaceae), Didiereaceae, Molluginaceae, Nyctaginaceae, Phytolaccaceae (including Agdestidaceae, Achatocarpaceae, Barbeuiaceae, Gisekiaceae, Petiveriaceae, and Stegnospermataceae), and Portulacaceae (including Hectorellaceae). In his classification, Cronquist (1981) considered Polygonaceae and Plumbaginaceae as the closest relatives of Caryophyllales, each in its own order and forming, together with Caryophyllales, the subclass Caryophyllidae.

The “classical” (betalain-producing) Caryophyllales or “core Caryophyllales” had been treated in 1993 in Volume II of this series (cf. Kubitzki et al.1993). At that time, very few results of molecular systematic studies were available and here the opportunity is taken to review their phylogenetic relationships, together with those of the non-betalain Caryophyllales which since have been added to this group.