The Hain Celestial Group has purchased a manufacturer of organic and gluten-free foods for $61.3 million. The Lake Success-based natural foods company said it had bought Rudi’s Organic Bakery Inc., based in Boulder, Colo., from the investment firm Charterhouse Equity Partners LLC. The acquisition expands Hain’s already substantial presence in the market for organic and gluten-free foodstuffs, company chief executive Irwin D. Simon said earlier this week. Rudi’s “expands our participation into 11 of the top 20 natural categories in the United States,” he said. Simon also said he hopes to add to Rudi’s current product offerings of bread, buns, bagels, tortillas, wraps, pretzels, pizza crust, stuffing and snack bars. Its sales totaled $60 million last year. Hain has had operations in Boulder since the 1960s but last year moved some accounting and research operations from there to its new, $10-million headquarters and product development center in Lake Success. The company’s Celestial Seasonings teas and WestSoy tofu are still made in Boulder.