Morphology, anatomy and germination response of heteromorphic achenes ofAnthemis chrysanthaJ. Gay (Asteraceae), a critically endangered species

Abstract

This study demonstrates that Anthemis chrysantha, a 'Critically Endangered' annual plant, produces two morphs of achenes: white and dark achenes, which differ in size, mass, anatomy and germination behaviour. Fresh white achenes germinated at all temperatures assayed from 10 to 258C in both continuous darkness and 12-h photoperiod, ranging between 24% at 258C in darkness and 89% at 12/208C in light, whereas fresh dark achenes did not germinate under any temperature or light conditions. To identify differences in dormancy type between the two morphs, germination of dry-stored achenes, and achenes stratified at 5 or 258C for 2 months were tested in both darkness and light at 5, 15 and 12/208C for drystored and warm-stratified (258C) achenes; and at 15, 25 and 12/208C for cold-stratified (58C) achenes. Of the white achenes, 90% germinated during the cold stratification period. In general, dry storage and warm stratification did not increase germination compared to fresh achenes. However, dark achenes did not germinate under any conditions. Dark achene dormancy was only broken by mechanical scarification or by excising the embryo (germination reached 71%). An anatomical study showed that the mesocarp of dark achenes had no intercellular spaces and was much thicker and stronger than that of white achenes, making the entry of water difficult, and also preventing germination by mechanical restriction. This study demonstrated that dormancy in the dark achenes is likely caused by the thickness of their pericarp, physically impeding germination and hampering imbibition of water.

Embryology of Ageratum conyzoides L. and A. fastigiatum R.M. King & H. Rob. (Asteraceae)

“…Phytomelanin was observed in some tribes of Asteraceae such as Carduoideae (Pandey & Singh 1982), Vernonieae (Basak & Mukherjee 2003;Loeuille et al 2013), Gnaphalieae (Davis 1962a), Anthemideae (Aguado et al 2011), Heliantheae (Maheshwari & Srinivasan 1944), and Eupatorieae (Pandey & Singh 1983;. According to De-Paula et al (2013), the fibres of the pericarp are directly responsible for secreting phytomelanin in Praxelis diffusa; this fact will probably also be true in Ageratum, where phytomelanin is observed primarily near the fibres.…”

Aerial seed bank and dispersal traits in Anthemis chrysantha (Asteraceae), a critically endangered species

“…The germination response increased with increasing amounts of water provided, up to 20 mm, when >80% of achenes on the soil surface, and around 20% of the buried ones, had germinated. There were no statistically significant differences between the control treatment Aguado et al (2011).…”

“…The morphological differences between the two achene types are correlated with variations in their germinability. White achenes germinate to high percentages in many conditions, while basal dark achenes are strictly dormant (Aguado et al, 2011).…”

“…The trial was carried out in a laboratory at room temperature (18-20 • C). All achenes used in this experiment were white, as dark achenes are dormant and rarely germinate (Aguado et al, 2011).…”

Influence of seed dimorphism and provenance on seed morphology, dispersal, germination and seedling growth of Brachyscome ciliaris (Asteraceae)

“…In the Chenopodiaceae, it is common for some species of Atriplex and Chenopodium to produce non-dormant brown seeds and dormant black seeds on the same plant (Harper et al 1970). Likewise, in Anthemis chrysantha (Asteraceae), non-dormant white seeds are produced, as well as dormant dark seeds (Aguado et al 2011). These variations in dormancy within a species are interpreted to be a form of bet-hedging against future catastrophes (Evans and Dennehy 2005).…”