Dimensions of pith, vascular tissue, cortex, live leaf bases, and periderm layers comprising the diameter of the stems of six Cycas species were measured at the standardized stem height where two vascular cylinders existed. The six species represent a range in susceptibility to injuries that occur in routine horticultural operations. We assigned a subjective numeric ranking from 1 for difficult to 10 for easy and then determined if this ranking correlated with any of the dimension characteristics. Pith diameter and cortex width differed among the species with the highly sensitive C. macrocarpa Griff. exhibiting the widest pith and most narrow cortex. Width of tissues peripheral to the vascular tissue (cortex, leaf base, and periderm layers) also differed among the species as did the proportion of total stem diameter occupied by these peripheral tissues. The sensitive C. macrocarpa exhibited the smallest values for these two variables. Simple correlation and multiple regression analyses indicated cortex width, total stem diameter, absolute width of peripheral tissues, and the relative proportion of these peripheral tissues in relation to stem diameter were positively correlated with susceptibility ranking. Of these, the relative proportion of peripheral tissues emerged as the variable with the most significant association with susceptibility ranking. Among these six representative species, the species that tend to be least susceptible to injuries during horticultural operations protect the youngest vascular tissues within a relatively wide zone of peripheral tissue. In contrast, the sensitive species exhibit a narrow zone of protective peripheral tissues.
Thomas E. Marler, Anders Lindström, and Jack B. Fisher
Thomas E. Marler, Anders J. Lindström, and L. Irene Terry
The extent of Chilades pandava Horsfield herbivory among 85 Cycadaceae species was determined by three evaluators in a common garden setting in Thailand to identify patterns that may improve horticultural and conservation management practices. The significant differences in herbivory damage from this invasive lepidopteran pest ranged 8.7-fold among the species. Phylogenetic sections of this monogeneric cycad family did not correspond to the relative differences among the species, and country of nativity was also not informative for this purpose. We suggest the Cycas L. species that share native habitat with this butterfly or the closely related Theclinesthes onycha Hewitson are among the least damaged taxa when they are comingled with other Cycas species in a common landscape. Grouping the most damaged Cycas species together in a managed landscape may reduce costs associated with plant protection. The inclusion of non-native Cycas plants in gardens nearby native Cycas habitats carries the potential of disrupting the delicate specialist relationship that native butterfly populations have with host Cycas species.
Jack B. Fisher, Anders Lindström, and Thomas E. Marler
We made drill holes in the stems of six Cycas species and used a standard microtechnique and microscopy methods to determine the structural responses of the soft-wooded, parenchymatous (manoxylic) stems after 2 and 12 months of recovery. We also injected an aqueous stain to one plant per species to determine the transverse hydraulic pathways among the discrete tissue categories. Expanding secondary tissue decay and insect larva infestations were evident in some wounds after 2 months. Wounds that lacked the secondary complications had recovered as a result of wound periderm after 2 months. Large areas of secondary rotting after 2 months were bounded by wound periderm after 12 months. The wound periderm formed a thick, leathery phellem (cork) that was continuous across cortex, vascular, and pith tissues. The six species represent a range in ease of horticultural management, yet the form of recovery from the wounds was similar for all species. Mucilage exudation from cut surfaces was copious, and species differences in volume of mucilage were also not related to extent or form of recovery from the wounds. Stain injected into the hole moved longitudinally and laterally within a vascular cylinder to adjacent vascular cylinders and to the cortex by way of persistent leaf traces. Results indicate a transverse hydraulic connection among the concentric vascular cylinders and leaf traces that extend into the cortex. Moreover, the succulent nature of this manoxylic stem is highly susceptible to secondary infection whenever the protective bark is removed or the internal tissues are injured. Therefore, use of prophylactic treatments to minimize the risk of secondary complications is warranted whenever pruning or amputation of adventitious shoots for propagation remove the protective bark from the succulent cortex tissue.
Benjamin E. Deloso, Anders J. Lindström, Frank A. Camacho, and Thomas E. Marler
The influences of indole-3-butyric acid (IBA) concentrations of 0–30 mg·g−1 on the success and speed of adventitious root development of Zamia furfuracea L.f. and Zamia integrifolia L.f. stem cuttings were determined. Root formation success for both species was greater than 95%. The IBA concentrations did not influence the speed of root development for Z. furfuracea, but the Z. integrifolia cuttings that received IBA concentration of 3 mg·g−1 generated adventitious roots more slowly than the cuttings in the control group. The ending dry weights of the stems, leaves, and roots were not influenced by IBA concentration for either species. Our results indicated that adventitious root formation on stem cuttings of these two Zamia species is successful without horticultural application of IBA. Additional IBA studies are needed on the other 300+ cycad species, especially those that are in a threatened category.