Arundina graminifolia an exotic orchid that has become naturalized in Puerto Rico

A flower of the most common form

A flower of the dwarf form

A flower of the dwarf form in the middle of a group of canes of this orchid

A side view of the flower of a form that seems to be uncommon in the extreme

Excuse me for the poor photo but it is the only front view I have of this mysterious flower

Arundina graminifolia is an orchid native of Southeast Asia that has become naturalized in Puerto Rico.   It can be found in the wild from Sri Lanka and India on the Indian Ocean to the Caroline Islands and Tahiti on the Pacific Ocean.  It is a vigorous plant that has escaped cultivation in areas outside its natural geographical range for example the Hawaiian Islands and Puerto Rico.  In Puerto Rico it has been reported from moist areas in the east of the island.

I have seen it growing in gardens all over the island sometimes forming huge specimen plants.  The tallest plants I have seen were in cultivation right on the ground in gardens in the foothills of the Luquillo Mountains, some seemed to be close to seven feet tall.  There is a huge specimen plant growing in a garden that sits by the side of the road that goes from Utuado to Adjuntas that is notable due to the large number of flowers it can have at the same time.  The plants are known locally as bamboo orchid due to a fancied similarity between the tall canes of this orchid and the canes of the bamboo plant.

I have seen several variations of this plant growing in captivity.  The most common form of Arundina in Puerto Rico is the tall one that can grow to six feet or more.  This form is nearly ubiquitous in the gardens of orchid growers.  However a dwarf form has become very popular in the last few years and it not rare to see this form growing as a pot plant.  It can also grow into a large clump of stems but since it is just a few feet tall even large clumps can be accommodated in a limited space.  The flowers of the tall type and the smaller type are quite similar, they differ mainly in the way the flower are presented and in some details of structure of the lip.  In its native haunts there are several varieties that formerly were classified as different species, these are now considered variations of a single species. Recently a white flowered form is sometimes being offered for sale at orchid shows but I have yet to see one blooming in a local garden.

Intriguingly there is a fourth type of Arundina in Puerto Rico.  The lip of the flowers of these plants is very different from the two more common types.  I have searched to see if this type of Arundina has been reported elsewhere but so far it has been absent from the books and Internet sources that I have accessed.   As far as I know this mysterious Arundina type is not in wide cultivation and I have seen mature plants of this type only in one private garden.  I was told that this type of plant was found in a population of feral plants in the south east of the island.

This orchid is easy to cultivate in Puerto Rico and responds vigorously to good care.  To cultivate this plant you need a eight or ten inch wide pot to accommodate its rampant growth.  The media should be coarse and heavy to avoid having the pot tip over.  Cow manure is an excellent additive as a top dressing to the media in the pot.  You need to water this plant abundantly as this helps the plant achieve its tallest size.  Large vigorous plants can produce single or branched inflorescences that can produce blooms sequentially for weeks or even for months.  When the inflorescences stop producing flowers they produce small plantlets.

These little plants can be detached when they stop growing.  I put them in water to stimulate the production of roots.  When the small plants have several roots they are transplanted to a pot with a mixture of potting soil and compost that is kept moist until the plants have been able to develop a significant root system.  This plant root system tends to be superficial so when growing the tall type in a pot it is useful to have a stake in the pot to tie the canes.  Young canes don’t need staking to stay upright but canes seen to become weaker with age and prone to tip over. Once the plant produces its second cane it can be treated as an adult plant.  Unlike most orchids this one is easy to grow into a specimen plant in a comparably short time.