Fruit and seed structure in the ANA-grade angiosperms: Ancestral traits and specializations.

PREMISE: The representatives of the ANA-grade angiosperms demonstrate a diverse pattern of morphological characters, but their apocarpous gynoecium (except in Nymphaeaceae), composed of at least partly ascidiate carpels, the four-nucleate and four-celled female gametophyte, and the diploid endosperm (except in Amborella) are inferred to be plesiomorphies. Since the structure of fruits in Austrobaileyales is under-investigated, this research aims to fill this gap in these data, describing the carpological characters of ANA-grade taxa, and potentially illuminating the ancestral fruit and seed types of angiosperms. METHODS: The pericarp and seed coat anatomy was studied with light microscopy. The character optimization was carried out using WinClada software. RESULTS: The fruits of Austrobaileya, Trimenia, Kadsura, and Schisandra are determined to be apocarpous berries of the Schisandra type, with a parenchymatous pericarp and mesotestal (Austrobaileya) or exomesotestal seeds (other genera). Most inferred scenarios of fruit evolution indicate that the apocarpous berry is either the most probable plesiomorphic fruit type of all angiosperms, or that of all angiosperms except Amborellaceae. This inference suggests the early origin of the berry in fruit evolution. The plesiomorphic seed type of angiosperms according to reconstructed scenarios of seed type evolution was either a seed lacking a sclerenchymatous layer or an exotestal seed. CONCLUSIONS: The current research indicates that an apocarpous berry, and not a follicle, is a probable plesiomorphic character of the ANA-grade taxa and of angiosperms as a whole.

Mummified fruits of Canarium from the upper Pleistocene of South China.

Canarium L. contains approximately 78 species distributed in low to middle altitudes of the Paleotropics and northern Australia. Canarium fruit fossils are known mainly from Paleogene to Neogene of North America, Africa, and Eurasia. Here, we described a new species Canarium maomingense sp. nov. from the upper Pleistocene of the Maoming Basin, Guangdong, South China. Similarly to extant Canarium species, each of three locules of C. maomingense possesses two ovules, but only one or two of six ovules develop into a seed, indicating that the ovules undeveloped into seeds in Canarium species have existed at least since the late Pleistocene. The natural habitats of extant relatives and associated fossil plants suggest subtropical evergreen broad-leaved and mixed forests in the late Pleistocene of this region. Some special damage traces are observed on pyrene surfaces, indicating possible plant interactions with animals and fungi.

Fruit structure in Magnoliaceae s.l. and Archaeanthus and their relationships.

PREMISE OF THE STUDY: The family Magnoliaceae s.l. is a basal angiosperm family with two subfamilies-Magnolioideae and Liriodendroideae, which differ by the types and structure of their fruits and seeds. The late Albian genus Archaeanthus shares many features of its reproductive organs with Magnoliaceae s.l., but its pericarp anatomy was never studied in detail. A broad-scale carpological investigation of Archaeanthus and Magnoliaceae s.l. was undertaken to reveal the nature of the similarities in fruit structure and to reconstruct Archaeanthus pericarp anatomy. These data are important to determine the early stages of fruit morphogenesis and thus to clarify relationships of Archaeanthus to the taxa of Magnoliaceae s.l. METHODS: The pericarp anatomy was studied with light microscopy, SEM, and polarizing microscopy. KEY RESULTS: The dehiscent, polyspermous follicles shed from the receptacle of Archaeanthus share similarities with dehiscent follicles of Magnoliaceae s.s. and shedding nutlets of Liriodendron. The seeds of Archaeanthus are dorsiventrally flattened, ovoid, and encircled with a single circular wing. The pericarps of all the taxa studied are differentiated into exocarp (epidermis), multilayered mesocarp, and endocarp (fiber-like sclereids). The mesocarp consists of parenchyma with scattered secretory cells and sclereid clusters (Magnoliaceae s.s., Archaeanthus) or composed by sclerenchyma (Liriodendron). CONCLUSIONS: The specializations of dehiscent multifollicles of unknown Cretaceous ancestors for different modes of seed and fruitlet dispersal formed the basis for the differentiation of two evolutionary lines with their divergence occurring more than 100 million years ago: Magnoliaceae s.s. and the Archaeanthus-Liriodendroidea-Liriodendron line (Liriodendraceae s.l.) within the order Magnoliales.

Pericarp development and fruit structure in borassoid palms (Arecaceae-Coryphoideae-Borasseae).

BACKGROUND AND AIMS: The Borasseae form a highly supported monophyletic clade in the Arecaceae-Coryphoideae. The fruits of Coryphoideae are small, drupaceous with specialized anatomical structure of the pericarp and berries. The large fruits of borassoid palms contain massive pyrenes, which develop from the middle zone of the mesocarp. The pericarp structure and mode of its development in Borasseae are similar to those of Eugeissona and Nypa. A developmental carpological study of borassoid palms will allow us to describe the process of pericarp development and reveal the diagnostic fruit features of borassoid palms, determine the morphogenetic fruit type in Borasseae genera, and describe similarities in fruit structure and pericarp development with other groups of palms. METHODS: The pericarp anatomy was studied during development with light microscopy based on the anatomical sections of fruits of all eight Borasseae genera. KEY RESULTS: The following general features of pericarp structure in Borasseae were revealed: (1) differentiation of the pericarp starts at early developmental stages; (2) the exocarp is represented by a specialized epidermis; (3) the mesocarp is extremely multilayered and is differentiated into several topographical zones - a peripheral parenchymatous zone(s) with scattered sclerenchymatous elements and vascular bundles, a middle zone (the stony pyrene comprising networks of elongated sclereids and vascular bundles) and an inner parenchymatous zone(s); (4) differentiation and growth of the pyrene tissue starts at early developmental stages and ends long before maturation of the seed; (5) the inner parenchymatous zone(s) of the mesocarp is dramatically compressed by the mature seed; (6) the endocarp (unspecialized epidermis) is not involved in pyrene formation; and (7) the spermoderm is multilayered in Hyphaeninae and obliterated in Lataniinae. CONCLUSIONS: The fruits of Borasseae are pyrenaria of Latania-type. This type of pericarp differentiation is also found only in Eugeissona and Nypa. The fruits of other Coryphoideae dramatically differ from Borasseae by the pericarp anatomical structure and the mode of its development.