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Tracy Monique Magellan, Chad Husby, Stella Cuestas and M. Patrick Griffith

). CAS is highly detrimental to cycads. Since its introduction, thousands of cycads have been killed in the Miami area ( Mannion, 2003 ; Whitelock, 2002 ). CAS is also the greatest threat to the native population of fadang in Guam ( Marler and Muniappan

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Thomas E. Marler, Vivian Lee and Christopher A. Shaw

Consumption of Cycas micronesica seed tissue has been associated with the amyotrophic lateral sclerosis–parkinsonism dementia complex (ALS–PDC) of the Western Pacific. However, failures to document vital plant and neighborhood descriptors and pronounced variability in toxin concentrations noted within and among studies obfuscate decades of research on this subject. We discuss the theoretical and experimental constraints of plant tissue sampling in relation to human disease research. Comparisons are made between this approach and methods used throughout the history of ALS–PDC research, most notably very recent reports concerning β-methyl-amino-alanine. Methods for studying possible plant neurotoxins need to be standardized and must follow rigorous criteria to be valid in principle. Our discussions reveal why these criteria are essential and highlight the impact that natural variations have on environmental toxin quantification and interpretation. Past research on cycad toxins is deficient on experimental and theoretical grounds, and interpretation of published data is dominated by ambiguities. This area of study as conventionally conceived and carried out needs transforming. We argue that future empirical studies should honor appropriate plant science standards concomitantly with medical science standards. This dual focus will ensure appropriate sampling scheme, sample size, and reporting of background plant and community factors known to influence phenotypic plasticity.

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Thomas E. Marler and Aubrey Moore

Cycads are an ancient lineage of plants routinely referred to as “living fossils” ( Norstog and Nicholls, 1997 ; Seward, 1917 ). The genus Cycas exhibits the most primitive features from among all cycad genera, and these charismatic plants

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Vickie Murphy, Kimberly Moore, M. Patrick Griffith and Chad Husby

Cycads represent one of the earliest seed plant lineages, originating ≈300 million years ago. According to the 2010 International Union for Conservation of Nature (IUCN) Red List, 62% of the world’s cycads are threatened with extinction ( IUCN Red

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Judy Kay, Arantza A. Strader, Vickie Murphy, Lan Nghiem-Phu, Michael Calonje and M. Patrick Griffith

make this area of work a clear path forward for the modern public garden. Cycad species are broadly imperiled by habitat loss. An additional consistent threat to cycads remains illegal collection in the wild ( Donaldson, 2003 ). Cycads fascinate the

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Benjamin E. Deloso, Anders J. Lindström, Frank A. Camacho and Thomas E. Marler

( Kay et al., 2011 ). Proficient horticultural practices may particularly benefit plant species that are threatened with extinction or nearing extirpation in the wild. Cycads are the most endangered group of plants worldwide, with more than 63% of

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Thomas E. Marler and Leah E. Willis

Leaf gas exchange characteristics for 16 species of cycad were determined under field conditions in Miami, Fla. Net CO2 assimilation (ACO2) ranged from 4.9 μmol·m-2·s-1 for Lepidozamia peroffskyana Regel to 10.1 μmol·m-2·s-1 for Zamia furfuracea L. fil. in Aiton. Stomatal conductance to H2O (gs) was more variable, ranging from 85 mmol·m-2·s-1 for Cycas seemannii A. Br. to 335 mmol·m-2·s-1 for Encephalartos hildebrandtii A. Br. & Bouche. Transpiration (E) ranged from 1.7 mmol·m-2·s-1 for Cycas chamberlainii W.H. Brown & Keinholz to 4.8 mmol·m-2·s-1 for Encephalartos hildebrandtii. Highly variable E was more controlling of water-use efficiency than the less-variable ACO2. The difference between air and pinnae temperature ranged from 0.3 to 1.6 °C and was inversely related to mean gs among the species. The values within geographic regions representative of the native habitats of the species were highly variable. For example, two of the African species exhibited the highest and lowest values of water-use efficiency in the survey. Leaf gas exchange for the four largest species with arborescent growth form was less than that for the three small species with subterranean or short bulbous growth form. The diurnal variation in leaf gas exchange for Zamia furfuracea exhibited a two-peaked pattern with a distinct midday depression in ACO2 and gs. The ratio of dark respiration to maximum ACO2 for Zamia furfuracea was 0.04. As a group, the values for ACO2 and gs for these cycads ranked at the lower end of the range for all plants species.

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Thomas E. Marler and John H. Lawrence

also exhibit a pachycaulous stem and simple architecture and vary in damage and recovery to TCs ( Griffith et al., 2008 ). However, stem construction tissues and their internal organization are highly contrasting between palms and cycads (see Norstog

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Thomas E. Marler and Gil N. Cruz

-only protection on unhealthy infested trees provided the evidence that both source and sink behaviors were involved in this response of a native cycad tree to a nonnative specialist pest. Uninfested seeds on unhealthy infested trees exhibited carbohydrate

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Thomas E. Marler and Nirmala Dongol

Cycads are ancient gymnosperms that represent the most threatened plant group today ( Brummitt et al., 2015 ; Fragniere et al., 2015 ). Their resilience and history provide ecologists and conservationists the unique opportunity to gain insight into