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Thomas E. Marler and Nirmala Dongol

decisions. Our foremost objective was to quantify expansion rates of various components of leaves and strobili for the endangered Cycas micronesica and then determine if the growth patterns were amenable to being fitted with mathematical models. We then

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Thomas E. Marler and Nirmala Dongol

general survey of a range of cycad species revealed that the four sugars vary among organs and among species ( Marler and Lindström, 2014 ). Our objective was to quantify NSC pools in megagametophyte tissue in Cycas micronesica seeds from 6 to 28 months

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Thomas E. Marler

Cycas micronesica was listed as Endangered under the International Union for Conservation of Nature (IUCN) in 2006 ( Marler et al., 2010 ) and Threatened under the United States Endangered Species Act (ESA) in 2015 ( United States Fish & Wildlife

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Thomas E. Marler and Nirmala Dongol

Aulacaspis yasumatsui Takagi invaded Guam in 2003 ( Marler and Muniappan, 2006 ). At that time, Cycas micronesica ( Fig. 1A ) was the most dominant tree species in natural forests ( Donnegan et al., 2004 ). Furthermore, this native cycad species

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Thomas E. Marler, Ross Miller, and Aubrey Moore

micronesica K.D. Hill and Cycas revoluta Thunberg trees. These two Cycas species were widely planted throughout the urban landscape before the pest invasions, and the regionally endemic C. micronesica was a dominant forest species. Coccobius fulvus

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

horticultural requirements. Guam's Cycas micronesica K.D. Hill is the island's only native gymnosperm and America's only native Cycas species. Exposure to secondary metabolites that act as neurotoxins via direct ingestion of seed gametophyte tissue from

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Trenton Hamada, Irene Terry, Robert Roemer, and Thomas E. Marler

arrival ≈4000 years ago ( Athens and Ward, 2004 ). Cycas micronesica K.D. Hill (Cycadales: Cycadaceae), Guam’s only native gymnosperm and a member of the C. rumphii species complex, likely arrived by floating seeds. C. micronesica is also found on

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Thomas E. Marler and Christopher A. Shaw

, Cycas micronesica K.D. Hill, provides a striking specimen plant in the urban landscape. Louis de Freycinet led a French scientific expedition on Guam for several months in 1819, and his records indicate that this taxa was among the most commonly planted

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Thomas E. Marler

Cycas micronesica is a tropical cycad species that is endemic among several western Pacific islands ( Hill, 1994 ). Paleoenvironmental investigations document its prevalence in Guam for more than 9000 years ( Athens and Ward, 2004 ). This tree has

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Thomas E. Marler

Cycas micronesica is an arborescent cycad with sclerophyllous, long-lived compound leaves that are produced in synchronized pulses. The photosynthetic characteristics of leaves in two sequential cohorts of ≈2 and ≈11 months after leaf expansion were determined in this study. Fluorescence yield following 30-min of light exclusion or from leaves engaged in photosynthesis under ambient light was measured throughout several 24-h periods to determine maximum quantum efficiency of PSII photochemistry and quantum efficiency under ambient light. Maximum quantum efficiency was similar for the two cohorts throughout the nocturnal period. Maximum quantum efficiency and quantum efficiency under ambient light declined following exposure to daily direct sun but recovered quickly each afternoon. This daily decline was greater for the older cohort than the younger cohort. Net carbon dioxide assimilation (Pn) was also determined using gas exchange, and light saturated Pn of the older cohort was 75% to 85% of that for the younger cohort during the daily maximum at late morning. Pn of the older cohort increased more slowly in the morning and declined more rapidly in the afternoon than did Pn of the younger cohort. Apparent quantum yield determined by gas exchange was similar for the two cohorts in the absence of extended sun exposure. However, this characteristic declined during midday, and the decline was greater for the older cohort. These results indicate that photosynthetic capacity of older C. micronesica leaf cohorts remains high, and these older leaves may substantially contribute to the plant's overall carbon economy. However, the number of hours during the day in which these older leaves reach their photosynthetic capacity is less than for the younger leaves.