Looking around at the hundreds of orchids in bloom on the back patio of her Weston home, Sara Singer is hard-pressed to pick a favorite from her beloved collection. There are the highly prized vandas, the pastel dendrobiums and the flat-flowered phalaenopsis. And don’t forget the paphiopedilums, commonly known as the lady slipper, that have pouches for pollination purposes. “I have every single type of orchid,” she said, laughing.