A cornucopia of diversity-Ranunculales as a model lineage

Abstract

The Ranunculales are a hyperdiverse lineage in many aspects of their phenotype, including growth habit, floral and leaf morphology, reproductive mode, and specialized metabolism. Many Ranunculales species, such as opium poppy and goldenseal, have a high medicinal value. In addition, the order includes a large number of commercially important ornamental plants, such as columbines and larkspurs. The phylogenetic position of the order with respect to monocots and core eudicots and the diversity within this lineage make the Ranunculales an excellent group for studying evolutionary processes by comparative studies. Lately, the phylogeny of Ranunculales was revised, and genetic and genomic resources were developed for many species, allowing comparative analyses at the molecular scale. Here, we review the literature on the resources for genetic manipulation and genome sequencing, the recent phylogeny reconstruction of this order, and its fossil record. Further, we explain their habitat range and delve into the diversity in their floral morphology, focusing on perianth organ identity, floral symmetry, occurrences of spurs and nectaries, sexual and pollination systems, and fruit and dehiscence types. The Ranunculales order offers a wealth of opportunities for scientific exploration across various disciplines and scales, to gain novel insights into plant biology for researchers and plant enthusiasts alike.

Keywords: Ancestral states; carpels; distribution; fossils; fruits; genomic resources; nectaries; phyllotaxy; phylogeny; sexual systems; spurs; symmetry.

Fig 1.

Simplified phylogeny of Ranunculales based on Wang et al. (2009), Ortiz et al. (2016), and Peng et al. (2023). Species for which major genomic resources are or will become available in the near future are next to their respective branches. Representative photos of Ranunculales flowers: (A) Aquilegia coerulea, (B) Thalictrum thalictroides, (C) Nigella damascena, (D) Staphisagria picta (Ranunculaceae), (E) Epimedium grandiflorum (Berberidaceae), (F) Pteridophyllum racemosum, (G) Capnoides sempervirens, (H) Eschscholzia californica, (I) Macleaya cordata, (J) Papaver somniferum (Papaveraceae). (Photo credit: A, D–G, H, J, Becker lab; B, Di Stilio lab; C, F, Jabbour; I, N, Pabón Mora.)

Fig. 2.

Simplified phylogeny of Ranunculales showing ancestral floral traits of the Ranunculales families.

Fig. 3.

SEM images of mature nectaries from four Ranunculales species: (A) Aquilegia coerulea (Ranunculaceae), (B) Epimedium grandiflorum (Berberidaceae), (C) Corydalis aurea (Papaveraceae), (D) Lamprocapnos spectabilis (Papaveraceae). Enlarged views of the nectary cells for Aquilegia and Epimedium are shown in insets. N, nectary; S, spur; St, stamen. Asterisks indicate swelling epidermal cells, and red arrowheads indicate active secreting cells. Scale bars: 100 μm (insets 10 μm).

Fig. 4.

Ancestral state reconstruction of gynoecium (left) and fruit (right) characters based on a phylogeny using rbcL as the marker gene. Trait descriptions are from Cheng-Yih and Kubitzki (1993), Endress (1993), Kadereit (1993), Lidén (1993a, b), Loconte (1993), and Tamura (1993).