Saturday, 6 August 2011

Old Man's Beard

The Vila Velha state park in Parana is well worth a visit, with it's spectacular sandstone rock formations. Matching the bizarre geology are tumbles of grey vegetation hanging from the trees - this is "Barba de velho" / Spanish moss (Tillandsia usneoides). It is not actually a moss, but, perhaps strangely, a type of bromeliad, and grows on trees from where it can absorb nutrients and water from the air or from rainfall.

Tilandsia has long thin stems with thin, curved leaves up to 6 cm long, the whole plant hanging down for up to 6m in a tangled mass. It does produce seeds from tiny inconspicuous flowers, but it can also spread from stem fragments that blow in the wind or are carried by birds onto convenient tress.

You would have to be pretty desperate to try and eat it, the leaves are wiry and covered in tiny scales, but it does have its uses. Traditionally it was used to stuff mattresses, and even form cloth. In modern times it has found a role as a bioindicator of air pollution. Plants are transplanted from clean to test areas where they absorb heavy metals from the air (but, crucially, not from the soil) for later analysis. You can even get an idea of what type of air pollution is the problem, for instance Zinc, Barium and Calcium are indicators of traffic pollution (it used to be Lead, but not any more), whilst Cobalt and Mercury can come from metal processing plants.

Figueiredo et al 2007. Assessment of atmospheric metallic pollution in the metropolitan region of Sao Paulo, Brazil, employing Tillandsia usneoides L. as biomonitor. Environmental Pollution 145 279 - 292


Rohrerbot said...

You have me interested:) I've added this on my list of places to visit when we eventually get down to visit. Beautiful!

Ruth Stephen said...


Anonymous said...

Very interesting!