Urban weeds of México City. Floristic composition and importan families

Abstract

THE URBAN RUDERAL VEGETATION OF MEXICO CITY WAS DOCUMENTED WITH 311 BRAUN-BLANQUET RELEVES PLACED SYSTEMATICALLY. A TOTAL OF 256 SPECIES WAS FOUND, A LOW NUMBER WHEN COMPARED WITH EUROPEAN CITIES AND CONSIDERING THE HIGH DIVERSITY OF THE SURROUNDING NATURAL VEGETATION. THE LIST INCLUDES 26 NEW RECORDS FOR THE VALLEY OF MEXICO. THE HIGH NUMBER OF NEW RECORDS MAY BE PARTLY EXPLAINED BY A QUALITATIVE CLIMATIC CHANGE IN THE URBANIZED AREA, NOTABLY THE ABSENCE OF FROSTS. THE BOTANICA COMPOSITION IS ANALYZED AT FAMILY LEVEL AND COMPARED TO MAIZE FIELD WEED COMMUNITIES IN THE HIGH BASIN OF PUEBLA AND TLAXCALA, A NCAR-BY MAIZE-GROWING REGION. ASTERACEAE ARE MOST IMPORTANT IN BOTH TYPES OF WEEDY HABITATS; POACEAE, BRASSICACEAE AND CHENOPODIACEAE ARE MORE IMPORTANT IN THE RUDERAL VEGETATION THAN IN THE AGRESTAL TYPE, WHEREAS THE FABACEAE CONTRIBUTE RELATIVELY LITTLE TO THE URBAN VEGETATION. APPARENTLY, THE INSECT-POLLINATED FAMILIES ARE AT A DISADVANTAGE IN THE CITY, WHEREAS THE WIND-POLLINATED AND AUTOGAMOUS SPECIES ARE MORE FREQUENT AND DOMINANT. FRECUENCY DATA SHOW THAT THE FOUR MOST IMPORTANT FAMILIES ACCOUNT FOR TWO THIRDS OF ALL INDIVIDUAL OCCURRENCES IN THE URBAN ENVIRONMENT AND IN MAIZEFIELDS ONLY FOR ONE HALF.