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New data on endosperm development in the early-divergent angiosperm Trithuria (Hydatellaceae) indicate that double fertilization results in formation of cellularized micropylar and unicellular chalazal domains with contrasting ontogenetic trajectories, as in waterlilies. The micropylar domain ultimately forms the cellular endosperm in the dispersed seed. The chalazal domain forms a single-celled haustorium with a large nucleus; this haustorium ultimately degenerates to form a space in the dispersed seed, similar to the chalazal endosperm haustorium of waterlilies. The endosperm condition in Trithuria and waterlilies resembles the helobial condition that characterizes some monocots, but contrasts with Amborella and Illicium, in which most of the mature endosperm is formed from the chalazal domain. The precise location of the primary endosperm nucleus governs the relative sizes of the chalazal and micropylar domains, but not their subsequent developmental trajectories. The unusual tissue layer surrounding the bilobed cotyledonary sheath in seedlings of some species of Trithuria is a belt of persistent endosperm, comparable with that of some other early-divergent angiosperms with a well-developed perisperm, such as Saururaceae and Piperaceae. The endosperm of Trithuria is limited in size and storage capacity but relatively persistent. Key words: angiosperm evolution; embryo; endosperm; Hydatellaceae; seed development; synchrotron; Trithuria; waterlilies. doi: 10.3732/ajb.0900033

Gomortega keule (Molina) Baillon is a rare Chilean species classified as endangered and currently under conservation. Currently, conservation of this species is carried out by private companies and government agencies, but is done so based more on pragmatic criteria than scientifically based strategies. In this context, information concerning the genetic variability of the species among the different populations over its entire distribution range is incomplete, making it difficult to coordinate management and conservation strategies. Here we report a study to evaluate the genetic variability and population structure of G. keule over its entire distribution in Chile. Twenty-five ISSR primers for 223 individuals from 11 geographical populations were tested to evaluate genetic variability. Results showed a high level of genetic diversity for the species. A high level of genetic differentiation among populations was found, while genetic structure of the geographic populations was also shown by using STRUCTURE 2.1 software. Despite the fact that this species has been highly affected by human intervention and habitat destruction, a high level of genetic diversity was present. A likely explanation for this is that it reflects the previous distribution of this long-lived species and the current lack of sexual regeneration. Genetic diversity data must be considered in the development of a management strategy for further developing the protected areas, for identifying isolated small populations for conservation, and using larger populations with higher genetic diversity as seed sources for ex situ propagation and replanting. Key words: genetic fragmentation, genetic diversity, Gomortega keule, ISSR markers, tree conservation. Le Gomortega keule (Molina) Baillon constitue une espece rare menacee, presentement en observation. Actuellement, des entreprises privees et gouvernementales en assurent la conservation sur la base de criteres pragmatiques plutot que scientifiques. Ainsi, l'information sur la variabilite genetique de cette espece dans les differentes populations et sur l'ensemble de son aire de distribution demeure incomplete, ce qui rend difficile la coordination des strategies d'amenagement et de conservation. Les auteurs ont effectue une etude sur la variabilite genetique et les structures des populations G. keule, sur l'ensemble de son aire de distribution au Chili. Ils ont evalue 25 amorces ISSR sur 223 individus provenant de 11 populations geographiques, afin d'en determiner la variabilite genetique. Les resultats montrent une grande variabilite genetique chez cette espece. On observe egalement un haut degre de differenciation genetique au sein des populations ainsi que dans la structure genetique des populations geographiques, en utilisant le logiciel STRUCTURE 2.1. En depit du fait que cette espece ait ete fortement affectee par l'activite humaine, notamment la destruction d'habitats, on observe toujours un fort degre de diversite genetique. Ce qui pourrait expliquer cette situation, c'est qu'elle reflete la distribution ancienne de cette espece longivive ainsi que le manque de regeneration sexuelle actuel. On doit considerer les donnees sur la diversite genetique lorsqu'on developpe des strategies d'amenagement pour implanter de nouveaux sites de protection, afin d'identifier les petites populations isolees pour leur conservation, et en utilisant les populations plus etendues avec une plus forte diversite genetique comme sources de semences pour la propagation ex situ et la transplantation. Mots-cles : fragmentation genetique, diversite genetique, Gomortega keule, marqueurs ISSR, conservation des arbres. [Traduit par la Redaction], Introduction To understand the genetic status of tree populations it is necessary to study not only the genetic diversity patterns among populations (Herrera et al. 2005), but also the current [...]