title: Seed development in Trimenia (Trimeniaceae) and its bearing on the evolution of embryo-nourishing strategies in early flowering plant lineages.
abstract: OBJECTIVE
  Seeds of most families in the ancient angiosperm lineage Austrobaileyales produce a full-fledged genetically biparental embryo-nourishing endosperm. However, seeds of fossil and extant Trimeniaceae have been described as having a perisperm, a maternal nutrient-storing and embryo-nourishing tissue derived from the nucellus of the ovule. Because perisperm is also found in Nymphaeales, another ancient angiosperm clade, the presence of a perisperm in Trimeniaceae, if confirmed, would be congruent with the hypothesis that the first angiosperms used a perisperm in addition to a minute (nutrient-transferring) endosperm. •
  
  
  METHODS
  Seed development was studied from fertilization through maturity/dormancy in Trimenia moorei and in maturing fruits of T. neocaledonica. •
  
  
  RESULTS
  A persistent layer of nucellar tissue surrounds the endosperm but does not contain stored nutrients and does not function as a perisperm. The nutrient-storing and embryo-nourishing tissue in Trimenia seeds is an endosperm, as is the case in all other members of the Austrobaileyales studied to date. •
  
  
  CONCLUSIONS
  The absence of a perisperm and the presence of a typical nutrient-storing and embryo-nourishing endosperm in Trimeniaceae may represent the ancestral condition for angiosperms. However, the combination of a copious nutrient-storing and embryo-nourishing perisperm with a minute endosperm, as in Nymphaeales, remains a plausible plesiomorphic condition for angiosperms as a whole. In either case, the developmental and functional biology of the diploid endosperm of Trimenia (and other Austrobaileyales) differs markedly from the diploid endosperm of Nymphaeales, and is fundamentally similar to the triploid endosperms of most other angiosperms.
authors.affiliation: Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA 02131, USA. ned@oeb.harvard.edu
authors.forename: William E
authors.initials: WE
authors.lastname: Friedman
authors.forename: Julien B
authors.initials: JB
authors.lastname: Bachelier
mesh_terms: D005075:Biological Evolution; D019684:Magnoliopsida / Q000235:genetics* / Q000502:physiology*; D012639:Seeds / Q000033:anatomy & histology / Q000254:growth & development* / Q000378:metabolism; D013045:Species Specificity; D013213:Starch / Q000378:metabolism
chemical_list: D013213:Starch
keywords: Austrobaileyales; Nymphaeales; basal angiosperms; diploid endosperm; female gametophyte; perisperm