One-Seeded Fruits in the Core Caryophyllales: Their Origin and Structural Diversity

Abstract

The core Caryophyllales consist of approximately 30 families (12 000 species) distributed worldwide. Many members evolved one-seeded or conjoined fruits, but their origin and structural diversity have not been investigated. A comparative anatomical investigation of the one-seeded fruits within the core Caryophyllales was conducted. The origin of the one-seeded fruits and the evolutionary reconstructions of some carpological characters were traced using a tree based on rbcl and matK data in order to understand the ancestral characters and their changes. The one-seeded fruit type is inferred to be an ancestral character state in core Caryophyllales, with a subsequent increase in the seed number seen in all major clades. Most representatives of the ‘Earlier Diverging’ clade are distinguished in various carpological traits. The organization of the pericarp is diverse in many groups, although fruits with a dry, many-layered pericarp, consisting of sclerenchyma as outer layers and a thin-walled parenchyma below, with seeds occupying a vertical embryo position, are likely ancestral character states in the core Caryophyllales clade. Several carpological peculiarities in fruit and seed structure were discovered in obligate one-seeded Achatocarpaceae, Chenopodiaceae, Nyctaginaceae, Seguieriaceae and Sarcobataceae. The horizontal embryo evolved in only certain groups of Chenopodiaceae. The bar-thickening of endotegmen cells appears to be an additional character typical of core Caryophyllales. The syncarpy-to-lysicarpy paradigm in Caryophyllaceae needs to be reinterpreted.

On Some Regularities of One-seeded Fruits Evolution

“…The relations between the pericarp and fruiting perianth/involucre compose here under complexification (union) type [38], and not as substitution, apparent in several other groups-certain members of Nyctaginaceae [39][40][41], Dipsacaceae [42], where the pericarp is reduced almost completely, in the second family together with perianth. This study thus demonstrates that one-seeded indehiscent fruits in different taxa may correspond to different morphological-functional systems, differing both in composition (a system "fruit-seed" transforms to "flower-fruit-seed inflorescence-(flower)-fruit-seed" one), and by their interrelationships, substitution or structural complexification.…”

Taxonomy and chorology of Corbichonia (Lophiocarpaceae s.l.) with further description of a new species from Southern Africa

“…The seeds of Corbichonia species are typical for the core Caryophyllales (for more see Sukhorukov et al 2015), with hard seed-coat testa, thin tegmen with cells having bar-thickened walls, annular embryo and copious perisperm. Three species in Africa and Asia; all species are found in southwest Africa.…”

“…In the last decade many species of Caryophyllales have been intensively studied in relation to their reproductive structures, as well as flower and fruit evolution, with a view to improving the morphological delimitation of the higher-level taxa within the Caryophyllales (Brockington et al 2009, Ronse de Craene 2007, Kadereit et al 2010, Greenberg & Donoghue 2011, Sukhorukov & Zhang 2013, Sukhorukov et al 2015. It seems that some genera previously merged together as relatives [Macarthuria Hügel ex Endlicher (1837: 11) and Corbichonia (see for more : Pax & Hoffmann 1934), or many Molluginaceae in extended circumscription (Endress & Bittrich 1993)] show many similar carpological characters (capsule as fruit type, black and shiny seeds, hard seed-coat testa, occurrence of funicular seed aril, etc.…”

“…Regarding the large number of differences between Lophiocarpus and Corbichonia, the relationship of the latter genus to Lophiocarpaceae must be checked. (Brockington et al 2013) thyrsoid consisting of lateral dichasia (Eckardt 1974) Flower morphology sepals (5) to 8 (Sukhorukov et al 2015) verrucose, rarely ribbed, completely or partially with unlignified cells, layers 4 to 10 in inflated parts or ribs (Sukhorukov et al 2015) Seed arillus + (strophiole) absent …”

“…Seed-coat testa sinus-like, triangular in cross-sections, 50-65 μm, warty in upper part, with obliquely oriented stalactites (Sukhorukov et al 2015) alveolate, in most species 20-50 μm (ca. 80 μm in L. latifolius), with almost straight stalactites (Sukhorukov et al 2015) Ovary obturator placental (Hakki 2013) funicular (Hakki 2013) …”