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Sunday, October 8, 2017

Air Plants

Ball Moss

When the time of year arrives when leaves begin to fall and the landscape starts to appear a bit more barren, some things become more noticeable, even though they were present all along.  One such thing is epiphytes, or plants that grow harmlessly upon another plant (such as a tree), and derive moisture and nutrients from the air.  The word epiphyte comes from the Greek ‘epi’ meaning ‘upon’ and ‘phyton’ meaning ‘plant.’  Epiphytes differ from parasites in that they grow on other plants for physical support and do not necessarily negatively affect their host.  They are also called ‘air plants’ since they do not root in soil.  In central Texas, the most common epiphytes native to our area are Ball Moss (Tillandsia recurvata) and Spanish Moss (Tillandsia usneoides).  

Members of the Bromeliad or Pineapple family, neither of these plants are real mosses, but true plants with flowers and seeds.  Ball Moss is a scurfy herb with narrow leaves forming small, grayish ball-like clusters on the branches of deciduous trees.  In North America, it is native from Florida to southern Georgia, Texas, New Mexico, and Arizona, with a disjunct population in central Louisiana.  Slender, pale violet flowers appear on long bracts from June to August.  Ball Moss grows well in areas with low light, little airflow, and high humidity, which is why it is often found on shade trees in the South.  It photosynthesizes its own food by receiving water vapor from the air, nitrogen from bacteria, and other minerals from windblown dust.  Wind is also the main method of Ball Moss seed dispersal, and its plentiful seeds are armed with fine, straight hairs that cling well to wet or rough surfaces such as bark.

Spanish Moss

Generally growing upon larger trees such as Southern Live Oak and Bald Cypress, Spanish Moss forms a cascading mass of slender, scaly gray leaves.  These scales help the plant absorb water and nutrients, mostly from the minerals naturally leached from the foliage of its host tree.   Its specific name ‘usenoides’ means ‘resembling Usnea’, which is also known as Beard Lichen, but this plant is not a lichen either.  It grows in chain-like fashion to form hanging structures up to 20 feet in length, and bears tiny whitish-green flowers from April to June. Its primary range is the southeastern US, but is found as far north as Virginia, and it propagates both by seed and vegetatively with fragments carried by the wind to neighboring tree limbs.  Spanish Moss has been used for various purposes, including building insulation, packing material, and mattress stuffing.  It is still in use today for arts and crafts, and even in the manufacture of evaporative or swamp coolers.  These coolers contain thick pads of Spanish Moss that are pumped with water, with the cooling effect of evaporation caused by a fan that pulls air through the pad and into the building. 

Little evidence exists that Ball Moss 
harms the health of a tree.

There is a common misconception that these epiphytes are parasites, and that they harm the trees that serve as their hosts.  While trees that are heavily infested with these plants can have increased wind resistance and result in fallen limbs, there is little evidence among the botanist community that a reasonable presence of these plants have a noticeable effect on the growth or health of the tree.  In fact, the presence of these air plants serves as a benefit to many forms of wildlife by harboring small insects that provide food, supplying nesting material, and serving as shelter from the outside elements.