The suitability of cryopreservation for the secure, long-term storage of the rare and endangered species Cosmos atrosanguineus was investigated. Using encapsulation/dehydration of shoot tips in alginate strips, survival rates of up to 100 % and shoot regeneration of up to 35 % were achieved. Light and electron microscopy studies indicated that cellular damage to some regions of the shoot tip during the freeze/thaw procedure was high, although cell survival in and around the meristematic region allowed shoot tip regeneration. The genetic fingerprinting technique, amplified fragment length polymorphisms (AFLPs), showed that no detectable genetic variation was present between material of C. atrosanguineus at the time of initiation into tissue culture and that which had been cryopreserved, stored in liquid nitrogen for 12 months and regenerated. Weaned plantlets that were grown under glasshouse conditions exhibited no morphological variation from non-frozen controls.

Viburnum tinus is an evergreen shrub that is native to the Mediterranean region but cultivated widely in Europe and around the world. It produces ripe metallic blue fruits throughout winter [1]. Despite its limited fleshy pulp,[2] its high lipid content[3] makes it a valuable resource to the small birds[4] that act as its seed-dispersers [5]. Here, we find that the metallic blue appearance of the fruits is produced by globular lipid inclusions arranged in a disordered multilayer structure. This structure is embedded in the cell walls of the epicarp and underlaid with a dark layer of anthocyanin pigments. The presence of such large, organised lipid aggregates in plant cell walls represents a new mechanism for structural colouration and may serve as an honest signal of nutritional content. 639088 (S.V., Y.O., G.J.), a microMORPH Cross-Training Grant (M.S.A.), a Yale Institute for Biospheric Studies grant (M.S.A.), National Science Foundation (NSF)SF GRFP DGE-1122492 (M.S.A.), and NSF DBI 1907293 (M.S.A.). We would like to acknowledge the assistance of the Boulder Electron Microscopy Service in preparation and imaging the serial block-face, and the support of the Cambridge Advanced Imaging Centre and the NanoBio-ICMG platform (FR 2607) electron microscopy facility. We are grateful to Heather Whitney and Innes Cuthill for loan of equipment and to two anonymous referees for advice and comments which improved the manuscript.

Results support the synanthial hypothesis as the evolutionary origin of the reproductive unit. Thus, the basic reproductive unit in Lepironia is an extremely condensed pseudanthium, of staminate flowers surrounding a central terminal pistillate female flower. Early in development the reproductive unit becomes enclosed by a split-prophyll, with the whole structure subtended by a bract.

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