Conservatory Chronicles: The Sausage Tree

Update June 11: a reader asks if the fruits of the sausage tree are edible. No - it would be "like eating a doormat" - all fiber - according to our curator.

Matthaei-Nichols horticulture manager Mike Palmer reports on the progress of the sausage trees (Kigelia africana) in the conservatory at Matthaei Botanical Gardens. Palmer notes that there are two flower stalks on what he calls the “north” sausage tree. The compass point refers to the fact that there are two sausage trees, one on the north end of the tropical house and one on the south end. The presence of flowers on the north sausage tree indicates that we will eventually have new fruits on a plant whose gigantic, sausage-shaped fruits are perennially popular with visitors.

The Sausage Tree Back Story

What’s up with the flowers, and why does it matter that the north tree has flower stalks? A sausage tree (Kigelia africana) is self-incompatible, which means that the pollen of any flower from the same tree cannot successfully pollinate its own female flowers. Two trees that are not genetically identical are needed for cross-pollination to occur and for the plant to set fruit. Fortunately the north and south sausage trees are genetically different plants.

Above: Two sausage tree flowers, one with all its parts (A stigma and four anthers) and the other minus the anthers that contain the pollen that Matthaei-Nichols staff preserved in the freezer.

Adding another layer of complexity, the species of sausage trees in the Matthaei Botanical Gardens conservatory are bat-pollinated. Since we have no bats in the conservatory, mere humans—Matthaei-Nichols staff—must hand-pollinate the flowers, bringing pollen from one plant to the other to get fruits to form on each tree.

Above: The fruit of the sausage tree.

Finally, in order to fruit, two different sausage trees must also be flowering at the same time. Last year the north sausage tree didn’t flower at all, hence no new fruits. This year the two trees are a bit out of sync. Hedging his bets, Palmer collected and froze pollen from the south sausage tree when it was in bloom. When the north sausage tree finally blooms we can use the preserved pollen to pollinate it. “It works!” says Palmer, who has used the technique before.