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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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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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Claudia Calonje, Chad Husby, and Michael Calonje

As a result of the vulnerability of wild cycad populations to human impacts, including collection for commercial horticulture, the Cycad Specialist Group of the International Union for Conservation of Nature (IUCN) recommends concerted efforts to

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Thomas E. Marler and Christopher A. Shaw

Contemporary cycads form a primitive plant group, and research on this group may yield increased understanding of many aspects of plant biology ( Brenner et al., 2003 ). The study of cycad taxonomy has received recent attention, and the result is a

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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, 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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Bijan Dehgan, Joseph E. Durando, and Thomas H. Yeager

Cycas revoluta, an important ornamental palm-like plant of warmer regions of the world, often exhibits a foliar chlorotic/necrotic dieback in landscapes. Despite a weak correlation (r2 ≤ 0.28) of percent symptoms with soil nutrient levels or pH, symptom severity was correlated more notably (r2=0.49) with Mn and had even a higher correlation (r2 = 0.61) with the Fe : Mn ratio. Anatomical examination of chlorotic leaflets indicated an accumulation of tanniniferous cells but did not provide direct evidence of Mn deficiency. Although field surveys indicated a link between low Mn levels and Fe : Mn ratio in the plant and appearance of the disorder, the manifestation of symptoms could not be directly correlated with any edaphic factors. However, identical symptoms were induced in young plants by withholding Mn in a solution culture experiment. Application of chelated Mn on expanding leaves alleviated the disorder, but only for the current growth flush. Irrigation frequency in concert with other cultural practices probably are more responsible for development of symptoms than actual soil Mn inadequacy. In consideration of acute susceptibility of cycads to micronutrient deficiencies, plants should be supplied with a complete micronutrient fertilizer during growth in containers and before field planting.

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Thomas E. Marler, Anders Lindström, and Jack B. Fisher

Several cycad species have entered the horticulture industry with Cycas revoluta Thunb. ( Fig. 1A ) represented more than any other taxa. All species of this group of dioecious gymnosperms are of value to collectors because of their ancient