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From: The Hawaiian Native Plant Propagation Database

Brighamia insignis - Propagation by seeds

Propagation by Seeds

The fruit of Brighamia insignis is a green capsule about 1/2 inch long which ripens six to eight weeks after pollination. When mature, the capsule splits open releasing many small, smooth seeds. Hannon states that the capsules may still be green when the open or they may have turned pale yellow or light cream in color. Some seeds may remain stuck to the sides of the capsule. The capsules can be harvested just as they start to crack open. Place the capsules in a paper bag or envelope until the seeds fall out of the open capsule.

Most sources state that Brighamia seeds require light to germinate and to sprinkle the seeds on the surface of moist, fine textured medium that drains well such as fine perlite or commercial peat/perlite potting mix. Hannon suggests a light covering of fine potting medium. Use of a mist system is suggested by NTBG. Seeds should be kept in partial shade. Koob indicates that the seeds will begin germinating in a couple of weeks and that most seeds will sprout at the same time. Christensen writes that the first seed germinated in 11 days and germination continued for 2 months. His final germination rate was 66%. Hannon reports sporadic germination beginning in two weeks. NTBG (Ragone 1993) reports 44% germination rate after 3 months for seeds stored for 5 months at 80 degrees F and 25% relative humidity.

Seed can be sown fresh or can be stored. Koob states that they can be kept in a refrigerator for up to 2 or 3 years. Hannon, however, writes that viability declines rapidly after 10 to 12 months. NTBG (Ragone 1993) reports that the seeds were no longer viable after storage at ambient temperature (80 degrees F) and relative humidity (25%) for 17 months. (Christensen 1979; Hannon 2002; Koob 2000; NTBG 1992; Ragone 1993; Wagner 1999)

Here is a link that might be useful: The Hawaiian Native Plant Propagation Database