Seeds from Phormium cookianum Mountain Flax. Despite its common name the New Zealand Mountain flax Phormium cookianum is found throughout New Zealand on coastal slopes above treeline, among scrub or grasses. Phormium cookianum is smaller than the New Zealand flax Phormium tenax and has more drooping leaves. Phormium tenax leaves are more stiff and erect. The seed capsules of the Phormium cookianum are drooping and twisted and not erect and angled as in P. tenax. The flowers are a source of nectar for the native birds, especially the tui and the bellbird. Most of the flax cultivars are derived from Phormium cookianum. Zones 8 to 10.