A broad expanse of gumplant, a hip-high bush bearing leathery green leaves, has not yet sprung its resin-topped flowers at the Giacomini Wetlands. But last Friday, a wetland biologist had no problem explaining what would happen come summer. “It oozes like glue, like Elmer’s Glue,” said John Callaway, a professor at the University of San Francisco . . .

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