This grower is fairly sure of this plant identification.
Clear pale yellow flowers with almost no markings
Iris, Flag iris, Fleur-de-Lys, Sword lily
Iris genus (Iris). This is a large genus of about 300 species which will produce upright, rhizomatous or bulbous perennials. Some are evergreen, but most are deciduous. The flower stems are usually unbranched. After the seeds you will find green then brown seed pods. Different species are adapted to diverse environments; borders, rock gardens, boggy ground, ponds, and woodland.
They are fully hardy, but some groups may thrive only in specific growing conditions. All irises are best planted in late summer and early autumn. Outdoors you can grow them in well drained, fertile, neutral or slightly acid or alkaline soil in full sun to lightly dappled shade. In order for irises to thrive, most of them need long, hot summers. Irises that require protection from rain or frost should be grown under glass.
Grown for their distinctive and colourful flowers. Suitable for coastal conditions.