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Background and Aims: Orchid seeds are reputed to be short lived in dry, cold storage conditions, potentially limiting the use of conventional seed banks for long-term ex situ conservation. This work explores whether Cattleya seeds are long lived or not during conventional storage (predried to ~12 % relative humidity, then stored at -18 °C)., Methods: We explored the possible interaction of factors influencing seed lifespan in eight species of the genus Cattleya using physiological (germination and vigour), biochemical (gas chromatography), biophysical (differential scanning calorimetry) and morphometric methods. Seeds were desiccated to ~3 % moisture content and stored at -18 °C for more than a decade, and seed quality was measured via three in vitro germination techniques. Tetrazolium staining was also used to monitor seed viability during storage. The morphometric and germination data were subjected to ANOVA and cluster analysis, and seed lifespan was subjected to probit analysis., Key Results: Seeds of all Cattleya species were found to be desiccation tolerant, with predicted storage lifespans (P50y) of ~30 years for six species and much longer for two species. Cluster analysis showed that the three species with the longest-lived seeds had smaller (9-11 %) airspaces around the embryo. The post-storage germination method impacted the quality assessment; seeds equilibrated at room temperature for 24 h or in 10 % sucrose solution had improved germination, particularly for the seeds with the smallest embryos. Chromatography revealed that the seeds of all eight species were rich in linoleic acid, and differential scanning calorimetry identified a peak that might be auxiliary to selecting long-lived seeds., Conclusions: These findings show that not all orchids produce seeds that are short lived, and our trait analyses might help to strengthen prediction of seed longevity in diverse orchid species., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Background: Orchid seeds are reputed to be relatively short-lived, although comparative studies across a wide range of storage temperatures and moisture contents are few., Objective: To explore how a wide range of temperature and moisture contents affects seed longevity in the orchid genus Cattleya., Materials and Methods: Seeds of three Brazilian orchid species in the genus Cattleya (C. amethystoglossa, C. kautskyana and C. tigrina) were subjected to controlled deterioration (CD) and seeds at three moisture levels were stored for up to 270 days at temperatures as low as -196 degree C. Seed ageing curves were constructed and seed quality assessed as germination level and speed index in vitro, and by tetrazolium staining. Seed morphometry, lipid content and composition were also determined., Results: Seeds were found to be lipid rich (54-70% DW) and short-lived under CD, with P50s varying less than two-fold (42 to 69 h) at 41 degree C. At cold (5 degree C) to ultracold (-196 degree C) temperatures longevity was greatest after pre-drying seeds to 15% RH, with germination varying by c. 6% after 270 days storage at these temperature limits. However, storage at -20 degree C resulted in a 5-46% reduction in germination, indicating a dry-seed sensitivity to conventional seed bank temperature. Ultra-dry (silica gel) and high humidity (82% RH) storage, in combination with various temperatures, compromised viability in one or more species. Overall, seed longevity in C. kautskyana > C. tigrina > C. amethystoglossa, which also reflected the pattern of embryo volume. The prospect that the generally shorter lifespans in orchid seeds may relate to stochastic processes the negative impact of which reach criticality sooner in smaller embryos requires further testing., Conclusion: Further evidence is provided that cryobiotechnology provides a biobanking option for orchid seeds with relatively short lifespans.