Frond

Frond

A frond is a large leaf with many divisions to it, and the term is typically used for the leaves of palms, ferns or cycads. [ [http://www.m-w.com/dictionary/Frond] - Merriam-Webster's Online Dictionary ]

A frond is the leaf- like structure of a fern or alga. The term is colloquially applied to the leaves of palms, cycads, and plants with pinnately compound leaves. A significant difference is that, unlike the leaves of the latter, fern fronds bear the reproductive structures (spore-bearing structures) of the sporophyte plant. Because many ferns grow fronds that are held more vertical than horizontal, the "upper" and "lower" surfaces of a frond are more correctly referred to as the adaxial and abaxial surfaces, respectively.

A fern frond consists of a stipe, the stem supporting the blade, and the blade consists of both a laminar (flattened) photosynthetic tissue and a rachis—that portion of the stem to which the laminar tissue is attached. The blades of fern fronds may vary from being simple (undivided) to being highly dissected, even "lace-like". If the leaf tissue is undissected, or the dissections do not reach to the "rachis", the frond may be described as lobed or "pinnatifid". Otherwise, the blade is compound and each large division of the laminar tissue arising from the rachis is called a pinna (pl., pinnae). The main vein or mid-rib of a pinna is known as a costa (pl., costae). Pinnae may be arranged along the "rachis" either directly opposite one another or alternating up the stem. The arrangement may change from the base of a blade to the tip, as in the example of "Blechnum" shown below (from base to tip: pinnae opposite to alternate, and pinnatisect to pinnatifid).

Many ferns have "pinnae" that are divided two or more times, and the level of division of the fronds is termed "pinnate" (or 1-pinnate), or "twice-pinnate" (2-pinnate), or the like. Each secondary division (division of a pinna) is termed a pinnule, and its mid-vein, a costule. A few species of ferns with divided fronds are not pinnate, but are palmate or bifurcate.

On some or all mature blades (usually on the "abaxial" surface) occur sporangia, which bear the spores. The sporangia are clustered in a sorus (pl., sori) or "fruit dot". Associated with each sporus in many species is a membranous structure called an indusium: an outgrowth of the blade surface that may partly cover the sporangial cluster. Fronds also may bear hairs or scales, glands, and, in some species, bulblets for vegetative reproduction.

Each frond arises from the stem or rhizome, which in most species is concealed in the ground or creeps along the ground (or branch or rock) surface. Growth of a fern frond differs from that of a leaf of a flowering plant. The fern frond unrolls from a tightly-coiled structure called a "fiddle-head" (see circinate vernation).

Some fern species feature frond dimorphism, in which fertile and sterile fronds differ in appearance and structure.

Footnote


Wikimedia Foundation. 2010.

Игры ⚽ Поможем написать реферат

Look at other dictionaries:

  • frond — frond; frond·age; frond·ed; frond·let; …   English syllables

  • Frond — (fr[o^]nd), n. [L. frons, frondis, a leafy branch, foliage.] (Bot.) The organ formed by the combination or union into one body of stem and leaf, and often bearing the fructification; as, the frond of a fern or of a lichen or seaweed; also, the… …   The Collaborative International Dictionary of English

  • frond — [frɔnd US fra:nd] n [Date: 1700 1800; : Latin; Origin: frons leaves ] a leaf of a ↑fern or ↑palm 1(2) …   Dictionary of contemporary English

  • frond — [ frand ] noun count a large long leaf divided into many narrow sections: fern/palm fronds a. a long narrow piece of SEAWEED …   Usage of the words and phrases in modern English

  • frond — 1785, from L. frons (gen. frondis) leafy branch, green bough, foliage. Adopted by Linnæus in a sense distinct from folium …   Etymology dictionary

  • frond — ► NOUN ▪ the leaf or leaf like part of a palm, fern, or similar plant. ORIGIN Latin frons leaf …   English terms dictionary

  • frond — [fränd] n. [L frons (gen. frondis), leafy branch, foliage] 1. a leaf; specif., a) the leaf of a fern b) the leaf of a palm 2. the leaflike part, or shoot, of a lichen, seaweed, duckweed, etc. fronded adj …   English World dictionary

  • frond|ed — «FRON dihd», adjective. having fronds: »fronded palms …   Useful english dictionary

  • frond — fronded, adj. /frond/, n. Bot. 1. an often large, finely divided leaf, esp. as applied to the ferns and certain palms. 2. a leaflike expansion not differentiated into stem and foliage, as in lichens. [1745 55; < L frond (s. of frons) branch,… …   Universalium

  • frond — UK [frɒnd] / US [frɑnd] noun [countable] Word forms frond : singular frond plural fronds a) a large long leaf divided into many narrow sections fern/palm fronds b) a long narrow piece of seaweed …   English dictionary

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”