Patterns of Variation in Foliar Trichomes of Eastern North American Quercus

Abstract

Scanning electron microscopy of leaf trichomes of the forty two native species of oaks in eastern North America indicates five patterns of variability: 1) Eight trichome types are evident among the species and each species possesses a definite complement of trichome types. Certain trichomes are restricted to particular subgenera and series. 2) An obvious seasonal loss of trichomes occurs during leaf maturation. This loss may be both quantitative in terms of trichome density and qualitative in terms of trichome type. 3) There is an obvious difference between the adaxial and abaxial surfaces. The adaxial side of most oak leaves is dark green, lustrous, and glabrous or glabrate. The abaxial surface either remains pubescent, becomes glabrate or glabrous, or maintains trichomes along the midrib or in the axils of major secondary veins. There are also initial quantitative and qualitative trichome differences between the two sides. 4) Geographical and ecological variations are due in part to non‐genetic ecophenic modifications, ecotypic differentiation, and random genetic differences not necessarily correlated with environmental conditions. Trichome types are considered to be less affected by environment than is trichome density. 5) Hybridization and introgression within a subgenus leads to localized variability. Trichomes of hybrids are usually a combination of the parental types. These five patterns of variation are predictable and appear to be held within rather narrow limits. The complement of foliar trichomes, therefore, is a reliable character in the taxonomy of the oaks.

Micromorfología foliar del género Quercus (Fagaceae) en México

“…The frequency of presence of the other trichome types did not differ very markedly between red and white oaks (Table 2). These patterns indicate that parallel losses and acquisitions of trichome types have occurred among the individual species and species groups in the genus Quercus (Hardin, 1979b).…”

“…Hardin, 1979b;Spellenberg, 1998). The samples analyzed in this study included a hybrid taxon, Q. x dysophylla and its two putative parental species, Q. crassipes and Q. crassifolia (Tovar-Sánchez and Oyama, 2004).…”

“…Bussotti and Grossoni, 1997;Valencia and Delgado, 2003), because it usually has a greater diversity of trichome types and therefore provides more characters for identification (Hardin, 1979b;Llamas et al, 1995). In this study, however, both the abaxial and adaxial leaf surfaces of the species were analyzed, as recommended by Hardin (1979b), because the quantitative and qualitative differences among the two surfaces may be a source of additional information.…”

Novel trichomes increase stamen stiffness in mung bean flowers

“…

(Hardin 1979). In addition, the presence or absence of a particular type of trichome on a plant appears to be an inherited trait (Lemke and Mutschler 1984).

The trichomes of mung bean described in this paper appear to have a function of conferring structural strength on a long cylindrical stamen.

…”

“…Des (Healy et al 1986). Also, the complement of trichomes on a plant can vary within a season as well as among species (Hardin 1979). In addition, the presence or absence of a particular type of trichome on a plant appears to be an inherited trait (Lemke and Mutschler 1984).…”