Ovule Morphology, Structure, And Development Features And Their Systematic Significance In Ranunculaceae

The ovule is vital in the angiosperms as a sexual reproductive organ. Many significant events of angiosperm life cycle, such as the initiation and development of female gametophyte, guidance for the pollen tube, the double fertilization, the development of the new sporophyte, are achieved in the ovule. Ranunculales is one of the most important groups in basal eudicots. Ranunculaceae, a core family in Ranunculales, is various in morphological characteristics, such as the leaves, flowers, carpels, and ovules. The variety of the ovules within Ranunculaceae may provide useful systematic information. There are some similarities and differences in molecular and non molecular systematic studies. The researches on ovule studies of Ranunculaceae may help us to understand the subfamilial, tribe, even genus relationships in Ranunculaceae.Mature ovules morphology of 42 species from 3 subfamilies, 11 tribes, and 25 genera of Ranunculaceae, ovules morphogenesis of 19 species from 3 subfamilies, 11 tribes, and 18 genera of Ranunculaceae, ovules histogenesis of 2 species from 2 subfamilies, 2tribes, and 2 genera of Ranunculaceae, were studied.1) Mature ovules morphology of 42 species from 3 subfamilies, 11 tribes, and 25 genera:The variety of the ovules within Ranunculaceae provide some useful information, the ovules of 36 species are anatropous; except Adonis, Ranunculus and Batrachium are hemianatropous.Mature ovules in genera of Subfam.Coptidoudeae and Subfam.Thalictroideae, Tribe Catheae, Tribe Adonideae, Tribe Callianthemeae, Tribe Nigelleae, Tribe Cimicifugeae and Tribe Delphineae of Subfam. Ranunculoideae are bitegmic integument; ovules in Tribe Helleboreae, Tribe Anemoneae and Tribe Ranunculeae of Subfam. Ranunculoideae are unitegmic integument.In bitegmic mature ovules, the inner integuments are all cup-shaped and the birms of the inner integuments are lobed; the outer integument of the most species is hood-shaped, except Aquilegia (Aquilegia ecalcarata) and Adonis are cupular-shaped. In unitegmic mature ovules, the integuments are cup-shaped and the brims of them are lobed in Tribe Helleboreae and Tribe Ranunculeae; the integuemnts are hood-shped and the brims of them are 3-lobed.In bitegmic mature ovules, the micropyles are endostomic except Aquilegia (Aquilegia ecalcarata) is atypical bistomic.In Coptis of Subfam. Coptidoideae, an appendage covers the ovule, and this kind of appendage was not found in other genera in the family. In Aquilegia, Dichocarpum, and Thalictrum of Subfam. Thalictroideae, the appedages are collar-shaped, or raphe-shaped, or ring-shaped and surrounding the funicles anyhow. In Subfam. Ranunculoideae, the ovules of most genera have no appendage except Tribe Helleboreae (Helleborus), Tribe Cimicifugeae (Eranthis), Tribe Callianthemeae (Callianthemum), Tribe Anemoneae (Anemone, Clematis, Pulsatilla) and Tribe Ranunculeae (Ranunculus, Batrachium, Ceratocephalus). In Helleborus and Eranthis, hood-shaped appendages form at the dorsal side of the funicle; in Callianthemum, a lamellar appendage arises on the ventral side of the funicle; in Anemone, Clematis, and Pulsatilla, the appendages arise on the ventral side of the funicle.2) Ovules morphogenesis of 19 species from 3 subfamilies, 11 tribes, and 18 genera:In bitegmic ovules, the inner integuments initiate annularly and become cup-shaped in maturity. The birms of the inner integuments are lobed. The outer integuments arise semi-annularly and become hood-shaped in maturity. But the ovules of Aquilegia (Aquilegia ecalcarata) and Adonis are different. The outer integument in Aquilegia ecalcarata initiates semi-annularly and becomes cupular-shaped in maturity. The outer integument in Adonis sutchuenensis initiates annularly and becomes cupular-shaped in maturity. In unitegmic ovules, the integuments in Helleborus, Oxygraphis and Ranunculus initiate annularly and become cup-shaped in maturity. The birms of the integuments are lobed. The integments in Anemone and Clematis initiate semi-annularly and become hood-shaped in maturity. The brims of the integuments are 3-lobed.3) Ovules histogenesis of 2 representive species from 2 subfamilies, 2tribes, and 2 generaThe epidermal cells of the base of nucellus divide and then form the inner integument andouter integument in Coptis chinensis and Caltha palustris.The nucellus derivation of the crassinucellate ovule (Coptis chinensis and Caltha palustris) are different, the nucellus of Coptis chinensis derive from the division of the nucellus epidermal cells and the parietal cell, but the nucellus of Caltha palustris derive from the division of the nucellus epidermal cells only.4) The variety of the ovules within Ranunculaceae may provide useful information for better understanding of the evolution of ovules. It has been considered that the anatropous, bitegmic, hood-shapde outer integument and endostomic clearly represent more primitive characters than the hemianatropous, unitegmic, cupular-shped outer integument and bistomic ones. The inner integument and outer integument of the ovules in Ranunculaceae may all derive from the epidermal cells of the base of nucellus division. But the nucellus derivation of the crassinucellate ovule are different, the nucellus of some species derive from the division of the nucellus epidermal cells and the parietal cell, but the nucellus of some species derive from the division the nucellus epidermal cells only.5) The ovule morphology studies support the subdivision of the family based on the molecular systematics, i.e. 4 subfamilies, Hydrastidoideae, Coptidoideae, Thalictroideae, and Ranunculoideae. The researches on ovule studies of Ranunculaceae also help us to understand the subfamilial, tribe, even genus relationships in Ranunculaceae. It has been considered that the genetic relationship of Thalictrum, Dichocarpum and Aquilegia are equal; a tribal rank for Helleborus and Callianthemum is reasonable; the affinity between Adonis and other follicular genera are weak; Anemone, Clematis, Pulsatilla and Hepatica were divided in different subtribes and different genera are reasonable; a genus rank for Oxygraphis and Halerpestes is reasonable, but Batrachium and Ceratocephalus should be regard as subgenus rank in Ranunculus.