Sunday, May 20, 2018

Are palms giant herbs?

The largest inflorescence in the world 
is that of a palm, Corypha
umbraculifera, which like the well-
known Century Plants in the New
World, dies after its massive
flowering.  The inflorescence
is said to contain approximately 
24 million flowers. 
Photo courtesy Scott Zona.

The  Palm Family (Arecaceae) includes some of the largest monocots in the world, and one could argue, the largest perennial herbs.

To call a massive palm tree an herb may seem like a strange statement, since it has a sturdy upright stem, and may live for 100 years or more. Palm trunks may be a meter or more in thickness (Roystonea or Jubaea), and they hold the records for the largest inflorescences (Corypha umbraculifera), the largest seeds (Lodoicea maldivica) and the largest leaves (Raphia regalis) in the plant kingdom.

The largest seed in the world, weighing
up to 55 pounds, is that of Lodoicea maldivica,
from the Seychelles Islands.  The large
seeds are thought to be an adaptation
for survival of seedlings in a thick forest
 with nutrient- poor soil. Posted on
Wikipedia, Creative Commons license.

Members of the genus Raphia in Africa have the largest leaves of any plant. Pictured is R. australis, which is truly huge,
but a camera-shy relative, R. regalis, has the largest leaves, measured at over 25 meters in length.
Photo posted on Wikipedia, Creative Commons  License.
So is a palm a herb? The traditional definition of a herbaceous plant (or simply herb, in a botanical rather than culinary sense) is that it lacks permanent, above-ground woody stems, though they may have woody underground parts. Tulips and dahlias are examples of perennial herbs, while pansies and marigolds are examples of annual herbs. The alternate category is woody perennials, which include trees, shrubs and lianas.  There are, in fact, some dwarf palms that do not produce upright stems.  They would clearly be perennial herbs.  But what about larger palms?

The  vegetation of herbaceous plants is produced entirely through primary growth, in which all tissues arise from the apical meristems, or buds, at the tips of the stems. In contrast, woody plants exhibit secondary growth both above and below ground.  It is important to note that wood is the production of concentric layers of secondary xylem.

Are bamboos, perennial herbs or trees? Photo by Alain Van den Hende,
posted on Wikipedia, Creative Commons License.
Tropical plants, and tropical monocots in particular, severely strain the distinction between those two categories. First of all, no monocot, even a palm "tree," has true woody tissues. Their stems, no matter how thick or dense, are produced entirely through primary growth, and are strengthened by dense masses of fibers, rather than by layers of secondary xylem.  For that reason alone, all monocots could be considered herbaceous.

Many botanists would consider that too picky, and would use the term "woody" in a broader sense to refer to the dense wood-like tissues of palms.  And there are a few monocots, such as the dragon trees, giant aloes and some dracaenas, that have a specialized form of secondary growth, but such growth adds only layers of fibers and vascular bundles, not layers of secondary xylem.

Even if we accept that palms and other giant monocots are trees, there are still many gray areas where one is not quite sure where herbaceous perennials end and trees begin, and so there is value in pointing out the distinction between the very different ways that monocots and dicots form tree-like growth forms (see The invention and reinvention of trees).

Monocots abandoned the ability to form true wood as their ancestors adapted to a growth form based on rhizomes, with leaves that elongate from the base, and short-lived upright reproductive shoots (see How the grass leaf got its stripes).  Leaves of monocots, which can  be relatively large, are heavily dependent on bundles of fibers for support against both gravity and wind, as well as sometimes for protection against herbivores.  As they spread to a wide variety of habitats, some monocots got larger and developed upright stems with increased density of supporting fibers.  Important commercial fibers come from a variety of monocots, including Manila hemp (from a type of banana), sisal (from a species of Agave), and New Zealand hemp (from Phormium).  Fiber can also be teased our of bamboo stems and the leaves, stems, and fruits of many palms. 

Tropical monocots tend to be evergreen, another way they differ from temperate herbs.  Banana plants, which are tree-like, but clearly herbaceous, remain above ground for several years.  Others, such as agaves, aloes, and birds-of-paradise have permanent tufts or rosettes of above-ground foliage, typically arising from underground rhizomes.  No one would confuse such plants with woody shrubs, and these must be considered  perennial herbs.   Other monocots, including many grasses (e.g. canes) have upright stems that are reinforced with fibers and may last for several years. Bamboos are giant grasses with sturdy upright stems that live for many years (see The grasses that would be trees).   Should they be called herbs or woody plants?  Neither, actually.

The whole point of this long diatribe is to once again to point out how different monocots are from other vascular plants.  Their growth forms cannot be classified in the same terms as dicots.  They have mimicked the forms of many other kinds of plants (e.g. palms vs cycads), but with very different patterns of growth and tissues. Some of the elaborate classifications of the past (try googling: "plant growth forms") included special categories for palms and bamboos, but many did not.  In my opinion, the term "woody" should not be used for any monocot.  We can substitute the word "fibrous," which will be much more accurate and informative.  Many tropical and xeric monocots can be referred to as evergreen perennial herbs.  That would cover agaves, aloes, yuccas, and birds-of-paradise, as well as smaller palms.  Tree-like monocots, such as coconut palms, bamboos, screw-pines, Joshua trees, and dragon trees, might be called "fibrous arborescent perennials."  

Wednesday, March 7, 2018

Mosses of Central Florida 52. Fontinalis sullivantii

Fontinalis sullivantii Lindberg (Fontinalaceae) is a straggling moss often found in water, but also on soil or tree bases in moist areas.  Leaves are spread primarily on two sides of the stem. Note all photos are of other species, provided to illustrate the general characteristics of the genus.

Fontinalis antipyretica, showing aquatic habitat.
Photo by Bernd Haynold, Creative Commons license,
posted on Wikimedia Commons
The stiff leaves lack a midrib, and the cells are worm-like, but plump, and densely filled with chloroplasts. A few cells at the base of the leaf are larger, more squarish, and clear.

Spore capsules appear along the stem and are nestled within a cluster of specialized leaves, lacking an elongate stalk.
The flattened leafy shoots of Fontinalis sullivantii.  Photo by
Kurt Stuber, Creative Commons license, posted on Wikimedia
The leaf tip of Fontinalis squamosa, showing the curvy,
worm-like cells filled with chloroplasts. 
Photo by Hermann Schachner, public domain, posted on
Wikimedia Commons

This species occurs throughout eastern U.S. and northern Europe.
It is found in northern Florida down to Hillsborough, Polk and Osceola Counties, though it has been sparsely collected.

Fontinalis may be confused with other aquatic mosses in Florida, but is distinguished from them by its lack of a midrib, the elongate, worm-like cells with thick walls, and the spore capsules that remain nestled within clusters of bract-like leaves.

Two other species have been collected sparsely in northern Florida: Fontinalis novae-anglae from the central Panhandle and possibly Orange County, and F. sphagnifolia, from central north Florida, with unconfirmed reports from Hillsborough and Polk Counties.  They differ in small, technical details.
The base of a leaf of Fontinalis antipyretica, showing larger,
clear, basal cells, captured nicely by Hermann Schachner, public
domain, posted on Wikimedia Commons.

Tuesday, March 6, 2018

Mosses of Central Florida 51. Leucodon julaceus

Leucodon julaceus (Hedwig) Sullivant (Leucodontaceae) forms colonies of erect leafy shoots arising from a branching stem system on tree trunks, logs, rock, and soil.
Photo by Scott Schuette, copyright MBG, posted on
Tropicos,  available under a Creative Commons License.

Leaves are short and scale-like, with inrolled edges, evenly distributed around the stem, and  lack midribs. Leaf cells are roundish-angular and largely smooth, but with some papillae on cells near the tip. When dry, the leaves press against the stem, resembling a tiny juniper twig.

Spore capsules are erect and egg-shaped, on short stalks arising from among specialized long, sword-shaped bracts, usually near the tips of the leafy shoots.

This species is found throughout the eastern U.S. and southern Ontario, as well as in Mexico and the West Indies.   It is found in northern Florida south to Hillsborough and Manatee counties.

It is somewhat similar to Schwetschkiopsis fabronia, but the latter is confined more to the bases of trees, and the leaves are "bumpy" throughout due to the translucent cell wall projections at the ends of cells.  Clasmatodon parvulus and Papillaria nigrescens are also similar but their leaves have distinct midribs.
Photo by Gerritt Davidse, copyright MBG, posted on
Tropicos,  available under a Creative Commons License.

Thursday, March 1, 2018

Mosses of Central Florida 50. Cyrto-hypnum minutulum

Cyrto-hypnum minutulum (Hedwig) W. R. Buck & H. A. Crum (Thuidiaceae)
is a creeping, freely branching moss found on rotting logs, the bases of trees, and rocks.
A dried specimen identified as Cyrto-hypnum minutulum in
USF Herbarium (Griepenburg s.n., 4 Apr 1970, Highland
Hammock State Park)

The leaves are scale-like, with small roundish to squarish cells with multiple papillae on both sides.  As in other members of the Thuidiaceae, leaves on the main stem are larger than on the branches.  The midrib extends 2/3 to 3/4 of the leaf length. Spore capsules are asymmetrical and bent to the side.

The related genus Thuidium differs in that papillae are found only on the lower surface, and there is usually only one per cell.

This species is found throughout state but lacking in the southern Atlantic counties.  It is also found throughout eastern N. America, Europe, and south into South America. 

Also found in Florida, but very limited in distribution and distinguished on minor characteristics are:
C. involvens, southern Florida north to Volusia County, but with major gaps.
C. pygmaeum, 2 records: Jackson and Manatee counties
C. schistocalyx : Highlands, Miami-Dade counties

The species has previously been known as Hypnum minutulum or Thuidium minutulum.

Wednesday, February 28, 2018

Mosses of Central Florida 49. Stereophyllum radiculosum

The flat, dried leaves of  Stereophyllum radiculosum have a
conspicuously bulging midrib.
Photo by Juan David Parra, copyright MBG, posted on
Tropicos,  available under a Creative Commons License.
Stereophyllum radiculosum (Hooker) Mitten (Stereophyllaceae) forms thin, flat mats on the base of trees, exposed roots, stumps, logs, and limestone,  The distinctive flat leaves are attached uniformly around the stem (not flattened in a plane), elliptic-ovate in shape, and somewhat contorted when dry. The midrib is strong and markedly bulging, but does not reach the tip.  The leaf cells are small, roundish, and contains a single papillum (translucent bump). Spore capsules are erect to somewhat leaning,  asymmetrically egg-shaped, and arise from the bases of the leafy shoot on relatively short stalks (0.6-1.2 mm).

The leaning, egg-shaped spore capsule of Stereophyllum.
Photo by Juan David Parra, copyright MBG, posted on
Tropicos,  available under a Creative Commons License.
This species is widespread in the tropics; found in the U.S. only in Alabama, Texas, and Florida, where it occurs in the southern part of the state as far north as Citrus, Volusia, and Alachua counties.

Most other creeping species found on tree bases have somewhat flattened shoots, with leaves mainly on two sides of the stem, and capsules strongly bent to the side (Isopterygium or Haplocladium) or symmetrical and upright (Sematophyllum, Entodon).

Monday, February 26, 2018

Mosses of Central Florida 48. Schlotheimia rugifolia

The distinctive brownish shoots of  Schlotheimia rugifolia.
Photo by Juan David Parra, copyright MBG, posted on
Tropicos,  available under a Creative Commons License.

Schlotheimia rugifolia (Hooker) Schwagrichen (Orthotrichaceae) forms distinctive reddish-brown mats on logs, tree trunks, and branches.  The leafy shoots are more or less erect (extending away from attached base).  The flat leaves twist spirally around the stem when dry.

The narrow-ovoid capsules are usually erect, but bent in this
dry specimen. Photo by Juan David Parra copyright MBG,
posted on Tropicos,  available under a Creative Commons

The leaves  of this species are elliptic, with short point at tip and have a slight rumpled (rugose) appearance. The midrib is strong, extending through to the short point.  Leaf cells are small, roundish, and smooth.  The spore capsules are erect and narrow-ovate in shape. They arise from the tips of the leafy shoots on elongate stalks,
Schlotheimia rugifolia  is found throughout the southeastern U.S. as far north as Virginia and Tennessee, and extensively in the New World tropics.  In Florida, it has been collected throughout the state but with gaps.  In particular, it has not been collected in any of the Atlantic coastal counties between Volusia and Miami-Dade.

This is one of the relatively few mosses found in Florida that occur relatively high on the trunks and branches of trees.  The dark, reddish brown coloring, the distinctive spiral twisting of the dried leaves and the longer capsule stalks will distinguish it from others, such as SematophyllumCryphaea, and Forsstroemia, in this habitat.


Tuesday, February 13, 2018

Mosses of Central Florida 47. Aulocomnium palustre

Aulacomnium palustre (Hedwig) Schwagrichen (Aulacomniaceae) forms tufted colonies of upright leafy shoots on wet soil, marshes, swamps, and sometimes rocks.  It employs asexual propagation via small, modified, bullet-shaped or spear-point leaves clustered at the tips of elongate stems.

The upright shoots of Aulacomnium palustre form loose tufts
on wet soil. Photo by Robert A. Klips.

The leaves are elongate, with a prominent midrib, and gradually come to a point.  Leaf cells are small, roundish and papillose.  Spore capsules are bent to the side, and distinctly grooved, but are not commonly seen in our area, as asexual propagation is abundant.

A single tapered leaf of Aulacomnium palustre, showing
the prominent midrib and tiny, rounded cells.
Photo courtesy Western New Mexico Herbarium,
from the Gila Wilderness.
This species is found in every state and province of North America and throughout the northern hemisphere.  In Florida it has been collected in scattered counties in the northern half of the state, as far south as Polk County.