The four-character silver-inlaid mark reads Ruyatang zhi, 'made by Ruyatang'. Ruyatang is very probably a studio name.
Pewter-encased Yixing teapots appear to have been invented by scholar-connoiseur Zhu Jian in the early 19th century, and Yang Pengnian was one of the finest makers of these pots at the time. These teapots inherited the simple and bold geometric shapes unique to Yixing pottery and effectively combined different materials such as pewter, jade and wood. The elegantly engraved calligraphic inscription and flower painting emphasised its association with the literati class, whose patronage during this period greatly elevated the status of Yixing teapots.
Compare the related pewter-encased examples of trapezoidal and oval shape with jade finials, handles and spouts included in the exhibition Yixing Purple Clay Wares from the K.S. Lo Collection at Flagstaff House Museum of Tea Ware, Hong Kong, 1994, nos. 43 to 45; and another example in the Victoria and Albert Museum illustrated in Rare Marks on Chinese Porcelain, Percival David Foundation, London, 1998, p.132, no.56