Submitted to: Proceedings of Guadalupe Mountains Symposium
Publication Type: Proceedings
Publication Acceptance Date: 1/1/2004
Publication Date: 11/1/2004
Citation: Tepedino, V.J., Griswold, T.L., Geer, S.M., Fitts, R.D. 2004. The reproductive biology of Mckittrick Pennyroyal, Hedeoma apiculatum (lamiaceae). Proceedings of Guadalupe Mountains Symposium 1998. Armstrong and KellerLynn, editors. National Park Service, Guadalupe Mountains National Park, TX. p.147-152.
Interpretive Summary: McKittrick Pennyroyal is a very rare mint that occurs in only a few populations in the Guadelupe Mountains of Texas and New Mexico. The species is listed as threatened under the Endangered Species Act. Its continued existence depends critically on the continued production of sufficient fruit and seed to enable present populations to replace or exceed themselves as they expire. Most rare plants produce fruits and seeds only with the help of flower-visiting pollinators such as native bees. When pollinators are required for the successful sexual production of rare plants, they must also be protected by land managers responsible for preserving plants. We studied the reproductive biology and pollinators of McKittrick Pennyroyal to determine whether flowers set fruit without being visited by pollinators, and to learn the identity of those pollinators. We learned that flowers must be visited to set the maximum number of seeds per fruit but that there is no difference between pollinator-mediated self- and cross-pollination. Important flower-visitors included several species of small, sweat bees and leafcutting bees, and painted lady butterflies. Experimental manipulations also showed that night-flying moths are important pollinators. Inclement weather was the cause of much reproductive failure.
Technical Abstract: We studied McKittrick Pennyroyal primarily at the Wilderness Ridge population in Guadalupe Mountains National Park. Bagging techniques that excluded insects from the flowers were used together with hand pollinations to elucidate the breeding system. The flowers are protandrous, with the initial male stage lasting one to two days depending on the weather. Because of their protandrous habit, flowers automatically self-pollinate (autogamy) uncommonly, even though they are fully self-compatible. Self-pollinations performed by hand produced as many fruits per flower and as many seeds per fruit as did hand cross-pollinations. Flowers did not set fruit parthenogenetically (agamospermy). There was no indication that fruit or seed production was being limited by inadequate deposition of pollen on receptive stigmas. The primary pollinators appear to be a variety of lepidopterans and bees. Experiments that allowed access to flowers only during the day or at night revealed that moths are as important pollinators as are butterflies and bees: there was no difference in fruit and seed production between flowers only open in day or night.