6 MISC. PUBLICATION 4 77, U. S. DEPT. OF AGRICULTURE 



COMPARATIVE KNOWLEDGE OF AREAS 



Central America in general is not nearly so well known as regards 

 Quercus as is Mexico. Yet, there are some areas in which extensive 

 collections have been made, and there probably remains little yet to 

 be discovered in the way of new species. Guatemala undoubtedly is 

 the best known country. The State of Chiapas in Mexico and the 

 Honduran countries are fairly well known, as is also Panama. There 

 are a large number of collections from Costa Rica, but many of its 

 problems are as yet very poorly understood. El Salvador and 

 especially Nicaragua are very poorly known. Very few species are 

 represented in the herbaria by more than two or three collections 

 from these countries, and most are known only from the type 

 collections. 



The very limited knowledge of the oaks of certain countries may be 

 attributed to the attitude of most collectors, since oaks are frequently 

 neglected by them because of being considered difficult to name or 

 because they labor under the misapprehension that fruiting specimens 

 are essential. Oaks are relatively difficult to name, but they will not 

 become less so unless they are collected for study. The species can 

 be named almost as readily from sterile specimens as from fruiting 

 specimens. It is very desirable to have fruit, and a very large collec- 

 tion totally lacking in fruiting specimens is sometimes rather trying, 

 but lack of fruit is no excuse for failure to collect oaks whenever the 

 opportunity presents itself. Flowering (staminate) specimens are 

 worthless unless they are accompanied by mature leaves by which 

 they may be identified. It is very desirable to collect flowering speci- 

 mens whenever they may be definitely associated with mature leaves, 

 in order that an analysis may be made of flowering characters. 



MORPHOLOGICAL BASIS OF CLASSIFICATION 



The differences in characters that have been used to characterize 

 and distinguish the various categories within the genus are described 

 and discussed as to significance and reliability in the following para- 

 graphs. 



Habit. — Although the various species of Quercus range from low 

 shrubs to giant trees, there is insufficient information on habit avail- 

 able to afford any aid in classifying the Central American species. 

 Some more northerly species are well known as strictly shrubby. 

 Others may reach maturity as either shrubs or medium-sized or even 

 large trees. Too frequently herbarium specimens are taken from 

 juvenile plants with the information recorded merely as "a shrub." 

 The data gleaned from herbarium labels have been recorded here 

 merely as a contribution toward the fuller information which must 

 eventually be gathered. 



Twigs. — The twigs of the current season offer the most useful stem 

 characters to be found. Although the thickness of the current twig 

 may vary a great deal between normal and excessively vigorous shoots, 

 the general trend of coarseness or of slenderness to be seen in a suffi- 

 ciency of normal material is a useful aid in recognizing a species even 

 though the exceptions often would bar its use in a key. The fluted 

 form of most twigs (the presence of longitudinal sulcae) is not of much 

 importance but has been included in the descriptions to serve for what 



