Foliar trichomes of gray-leaved Tillandsioideae (Bromeliaceae) are highly reﬂective, suggesting a role in protecting the leaf against direct sunlight in exposed niches. The performance of photosystem II, as denoted by the chlorophyll ﬂuorescence characteristic Fv /Fm , was determined for seven Tillandsia species and Vriesea barclayana that were exposed to excessive light, with trichomes either present or removed. Additionally, trichome structure and interaction with light was recorded using extended depth-of-ﬁeld photomicrography, and reﬂectance quantiﬁed using a novel photographic technique. Trichomes of mesomorphic Type IV life forms (T. cryptantha, T. cyanea) and of the intermediate life form V. barclayana conferred reﬂectance of between 1 and 11%, which did not signiﬁcantly inﬂuence Fv /Fm when exposed to a high light intensity of 1500 µmol m-2 s-1 (photosynthetically active radiation) for one hour. However, the ornate trichomes of atmospheric species increased the reﬂectivity of the leaf blade by as much as 18– 40%, with a positive correlation apparent between reﬂectance and photoprotection. Type V Tillandsia andrieuxii, T. caput-medusae, and T. mitlaensis have attenuated trichome wings extending perpendicular to the leaf surface and catching the light (with leaf surfaces appearing gray and fuzzy). This open conﬁguration was observed to facilitate leaf ventilation and the condensation of water vapor on the cooler underlying cuticle, with liquid water subsequently enveloping the trichomes, suggesting a trade-off between water acquisition and light reﬂectance for air plants from xeric habitats. However, Type IV-V T. albida and T. concolor impound water in leaf bases and the ﬂattened, circular, and overlapping trichome wings did not facilitate dew formation on the cuticle. For these plants with white, smooth leaf surfaces, trichomes are multifaceted and provide more effective photoprotection by scattering light in the manner of cut gemstones.
"The Jeweled Armor of Tillandsia—Multifaceted or Elongated Trichomes Provide Photoprotection,"
Aliso: A Journal of Systematic and Evolutionary Botany:
1, Article 6.
Available at: http://scholarship.claremont.edu/aliso/vol23/iss1/6