Excerpts from Jim Conrad's
Naturalist Newsletter

from the July 24, 2016 Newsletter issued from Hacienda Chichen Resort beside Chichén Itzá Ruins, central Yucatán MÉXICO
AN HERBACEOUS BAMBOO

With the rainy season's arrival the forest is dark and shadowy, and when an understory plant happens to be enjoying its moment in a sunbeam, it shows up as if beneath a spotlight. Such was the case with the knee-high grass shown below:

OLYRA GLABERRIMA, habitat

Anyone familiar with North American grasses might see a resemblance between this one's broad leaves and those of the big group known as the panic grasses. However, the flowering spikelets above the vegetative parts don't look like panic grass flowers, which are spherical to oblong. This is something new for us. A closer look at the leaves is shown below:

OLYRA GLABERRIMA, leaves

The bases of panic grass leaves tend to partly wrap around the stem, but here the blades' bases narrow as they approach the stem and don't embrace it at all. A closer look at a leaf base shows something remarkable, a field mark seldom seen among grasses, and that's a petiole-like structure, sometimes known as a pseudopetiole, shown below:

OLYRA GLABERRIMA, pseudopetiole

In that picture the blackish pseudopetiole at its bottom fuses with the top of the sheath that wraps around the stem below the point of blade attachment. Here we also see that the ligule at the top of the sheath consists of no more than a very low, thin membrane bearing a few extremely short and fine hairs, or cilia.

At the grass's base we find remains of stiff, somewhat woody stems from previous seasons, which brings to mind the bamboos, as you can see below:

OLYRA GLABERRIMA, semi-woody stem bases

Along with its unusual vegetative features, this grass's flowers, or florets, also are a little unusual, in that they are unisexual. We've come onto the grass exactly when each of its few, large female florets bears two exceptionally conspicuous, feathery styles, as shown below:

OLYRA GLABERRIMA, female flowers with branched styles

In that photo, the smaller florets above the large female ones are the unisexual male ones, at this moment not yet mature. Having its female flowers mature before its male ones assures that the grass's flowers don't self pollinate.

With such peculiar and easily seen field marks, this species was easy to identify as OLYRA GLABERRIMA, found in Mexico, Central America and western South America, including Brazil. Within the Grass Family, the Poaceae, the genus Olyra falls into the Bamboo Subfamily, the Bambusoideae, and tribe Olyreae, so we can think about it as a kind of bamboo.

A 2013 paper by Scot Kelchner and others in Molecular Phylogenetics and Evolution, reporting on gene analysis of numerous members of the Bamboo Subfamily, the Bambusoideae, found that species within the subfamily tend to fall into four major groupings: temperate woody, Old World tropical (paleotropical) woody , New World Tropical (neotropical) woody, and herbaceous bamboos. Our grass in the genus Olyra is considered as a member of the herbaceous bamboo group -- despite the fact that some technical descriptions describe the species as producing woody stems.

It's hard to say where herbaceousness ends and woodiness begins, but it's clear that our Olyra glaberrima is much more herbaceous than most other bamboos.

So, who would have thought it? An herbaceous bamboo...