CHICAGO — No longer do colorful leaves and cooler temperatures signal the start of fall — but rather a proliferation of pumpkin-flavored products on menus.

Click here for a slideshow of seasonal selections from restaurant chains.

By late August and early September, a number of restaurants already had begun offering autumnal items, from pumpkin spice lattes and pumpkin pie donuts to caramel apple cupcakes and Oktoberfest burgers.

“Society has started the holiday preparation early, and so have restaurants,” said Mary Chapman, director of product innovation at Technomic, a Chicago-based research firm. “That’s why we’re seeing pumpkins earlier and earlier, and we’ll see eggnog and peppermint and winter holiday flavors earlier and earlier.”

The gourd has soared on menus across the quick-service and casual dining landscape, popping up predominantly in desserts and beverages, such as coffee drinks, frozen treats and baked foods.

“More brands are promoting pumpkin and other seasonal flavors, and those who do are finding new ways to use it,” Ms. Chapman said.

A growing appreciation for fresh and in-season ingredients supports the trend, as well as the sentimentality associated with fall’s warm and spicy flavors. Apples, butternut squash, bourbon and sweet potatoes also are popular ingredients, and baked pastas, braised pot roasts and brats have replaced fish dishes and citrusy flavors on limited-time menus, Ms. Chapman said.

“Traditionally, as diners we want something a little more hearty (this time of year), so we think of items that are braised or baked or slow-cooked rather than something that’s light and grilled and light in flavor,” she said. “We want something that’s warmer.”

More than half of fast-casual customers said in a Technomic survey they are more likely to order an item described as “seasonal.” But while many may welcome the early arrival of autumn flavors, others may burn out by Halloween, Ms. Chapman said.