Volume 67 — Issue 2 (June 2002)

Ecological life cycles, growth characteristics, and flowering requirements of the two closely-related species Penstemon tenuiflorus and P. hirsutus were compared via a combination of field, greenhouse, and growth chamber studies. In addition, field observations were made on plant-animal interactions involving these two species. Both species are hemicryptophytes that reproduce by seeds and by vegetative offshoots, and their life cycle stages, phenology (where their ranges overlap in northcentral Tennessee), growth characteristics, and flowering requirements are the same. Plants flower in spring, and seeds are mature by late summer; seed dispersal lasts from late summer until early spring. Seeds germinate primarily in early spring, and plants form a rosette their first year; neither species forms a persistent seed bank. In a non-heated greenhouse, plants bolted and flowered in their second year, whereas in the field bolting and flowering are delayed until at least the fourth year. Neither net assimilation rate, relative growth rate, nor eight of 10 other parameters of growth differed between plants of the two species grown under greenhouse conditions. Plants of both species require exposure to several hundred hours of vernalizing temperatures to flower; however, they are indifferent to photoperiod with regard to flowering (i.e., day-neutral). Leaves of P. tenuiflorus are browsed by cottontail rabbits and inflorescences by whitetail deer, and seeds of both species are predated by lepidopteran larvae. Thus, the ecological life cycle, growth characteristics, physiological requirements for development, and plant-animal interactions are very similar in these two taxonomically-distinct species. It seems unlikely that any of these aspects of their autecology accounts for differences between them either in geographical distribution or habitat ecology.

Scrub vegetation reestablishes poorly in former agricultural sites. Between 1992 and 1999, we followed the survival and growth of scrub oaks, saw palmetto, and other species planted in a former citrus grove on scrub soil adjacent to extant scrub and also followed the changes in community composition. Oaks, (Quercus chapmanii, Q. geminata, Q. myrtifolia) were planted in the summer of 1992 with a second planting in the summer of 1993. Serenoa repens, Pinus elliottii, and ericads were planted in the summer of 1993. We relocated marked plants annually and determined survival and height growth. Mortality of oaks was concentrated in the first year. Survival and growth of Q. geminata were significantly greater than that of Q. myrtifolia or Q. chapmanii. Survival was lower but differences between species were similar in the second cohort of oaks. Initial survival of Serenoa was high but declined due to rooting by feral pigs. Serenoa grew slowly. Survival of Pinus elliottii was high and growth rapid. Soils (0-15 cm layer) of the former grove differed from that of adjacent, intact scrub, with higher pH, NO₃-N, available Cu and Zn, but lower organic matter, NH₄-N, available Al, and Fe. We determined changes in community composition by annual sampling of line-intercept transects. Cover of native, woody scrub species increased slowly. Herbaceous, weedy species remained dominant through 1999, and exotic grasses were an important component of the vegetation.

The woody communities of seven of the most intact bottomland hardwood forests of southeastern Louisiana are described. The seven forests are on old levee ridges associated with past distributaries of the Mississippi River. The communities were divided by diameter size class into overstory (≥10.0 cm dbh) and understory (3.0 cm ≥ 10.0 cm dbh). The overstory (27 species) and understory (24 species) shared 18 species out of a total of 33. The understory stratum in these forests was not as uniform as the overstory across the forests in both dominants and subdominants. The forests were divided into two groups based upon size and abundance of two dominant overstory trees, live oak (Quercus virginiana) and sugarberry (Celtis laevigata). Other important overstory taxa were water oak (Quercus nigra), red maple (Acer rubrum), sweet gum (Liquidambar styraciflua), and elm (Ulmus spp.). The average total overstory density for the forests was 358.5 stems/ha and the average total overstory basal area was 30.5 m²/ha. The effect of microtopography, with its impact on hydroperiod, along and across the levee ridges was likely the principal variable impacting species dominance and diversity across the forests. These forests are under severe threat and conservation of those still remaining is a priority.

The Trillium pusillum Michaux complex consists of five or six morphogeographical taxa distributed within the southeastern United States. A quantitative morphological study was undertaken to determine appropriate species and varietal ranks of these taxa, which have a confused taxonomic history. Numerical analyses based on 14 floral and vegetative characters measured from 29 populations of T. pusillum revealed significant differences among varieties. These exist, however, as arrays of characters rather than as single characters. All characters were highly variable within and among populations, suggesting that quantitative measurements alone are unreliable as distinguishing characters. We concluded that all of the previously recognized infraspecific taxa lack clear morphological separation. We therefore recommend recognition of a single variable species without varietal designations.

The Okee chobee Gourd, Cucurbita okeechobeensis (Small) L. H. Bailey, is a robust, often overwintering, herbaceous vine endemic to Florida. Though originally observed by William Bartram in 1774 along the St. Johns River, in the eastern peninsula, it has since been known only from the marshy shores of Lake Okeechobee, south-central peninsular Florida. It has now been rediscovered in small numbers, still extant along the St. Johns, where last seen by Bartram two and-a-quarter centuries previously.

Effects of shade, drought, and soil type on survival and growth of the two closely-related species Penstemon tenuiflorus and P. hirsutus were compared in a greenhouse study. Eighty to 100% of 15 replicate plants of P. tenuiflorus and 60% to 93% of 15 plants of P. hirsutus survived in the three light levels under which they were grown, i.e., no shade, intermediate shade, and heavy shade. Plant dry mass (root, shoot, total) decreased with increase in shading: no shade > intermediate shade >> heavy shade. For a given level of shading, there were no significant differences between the two species for any of 12 plant growth variables measured. In a 30-day drought experiment during which soil moisture decreased to the permanent wilting percentage on day nine, four and three of five replicate plants of P. tenuiflorus per treatment, and four and one of those of P. hirsutus, survived the 18- and 21-day drought, respectively; no plants of either species survived the 24-, 27-, or 30-day droughts. Of the five soil types tested, plants of both species survived and grew best in greenhouse soil (high P) and worst in black shale soil (very low pH). Plants of P. hirsutus grown in greenhouse soil and in sandstone soil produced significantly more dry mass than did those of P. tenuiflorus in these soil types. Amount of growth was relatively low for plants of both P. tenuiflorus and P. hirsutus grown in native cedar glade and limestone-ledge soils (both with very low P), respectively. This study suggests that P. tenuiflorus is a bit more tolerant to drought than is P. hirsutus, whereas P. hirsutus has the ability to grow better on a greater variety of substrate types than does P. tenuiflorus. The major findings of Parts I-IV of this comparative study of the biology of P. tenuiflorus and P. hirsutus are sum marized.

In a continuing study of the biodiversity and biogeography of poroid wood-decay fungi in North Carolina, a notable number of species and fungus-host combinations previously not reported in the state were collected. Eleven species of poroid wood-decay fungi are reported as new in North Carolina. Eighty-five species are reported on a new host plant species resulting in 315 new fungus-host associations in North Carolina, of which 231 are new fungus-host associations for the United States.

Virginia bunchflower (Melanthium virginicum L.) is known historically from wet-mesic prairie in 17 counties located primarily in west-central Illinois. Due to the loss of wet-mesic prairie, plants within six counties were extirpated during the 1800s, and populations within an additional six counties were extirpated within the last 15 years. This taxon is currently known from thirteen populations in three counties. These populations were studied over a three year period, beginning in 1998 and ending in 2000. Flowering varied considerably from year to year. Although large bunchflower colonies remain that contain over 800 plants, only two populations are currently protected. Population loss is expected to continue, documenting the need for greater protection and the introduction of this plant into suitable wet-mesic prairie restorations within its historic range.

Noteworthy Collections: North Carolina, Arkansas, Texas, Alabama, and Michigan

Based on years of field experience with orchids and many thousands of miles of travel in Florida, Mr. Brown’s book is a wonderful addition to the library and field kit of anyone interested in wild orchids of the southeast. Included are line drawings, distribution maps, keys, more than 440 photographs, and detailed descriptions of 117 orchid taxa of Florida and nearby states in the southeastern coastal plain. The introductory material is an outstanding resource, including a quick lesson in “how to use a dichotomous key” that moves into a useable and nicely illustrated key to genera.