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Field Trip to Victoria Peak for Bryophytes and Lichens

 

1            Introduction

 

Victoria Peak is the tallest peak on Hong Kong Island, reaching 554 m above sea level.  It has been well protected from fire and cutting in the last few decades.  A fair collection of herbs and small trees are found there, and are maintained by the underground water and morning fog.

 

Since the Peak can be easily reached by bus or tram, teachers are likely to bring their students to this site for picnic and outing.  This exercise is part of the series to get teachers acquainted with the plants on Victoria Peak. It aims to (a) provide a general background on the biology, importance and adaptations of bryophytes and lichens; and (b) supply a simple and quick approach to identify major groups and common species of bryophytes and lichens on the Peak.

 

1.1              What are bryophytes (苔蘚植物)?

 

Bryophytes, comprising mosses (蘚類), liverworts (苔類) and hornworts (角苔類), are a group of small, green land plants characterized by (a) the absence of vascular tissues and by (b) the unique life history having a dominant gametophyte generation (配子體世代), which produces the sex organs (antheridia and archegonia) and gametes (sperms and eggs). The sporophytes (孢子體), which produce spores, cannot live alone and is essentially dependant on the gametophyte for water and nutrients.

 

Bryophytes are the second largest group of land plants, followed angiosperms, with about 15,000 species worldwide. They can be found in most terrestrial and some fresh water habitats except marine environment. They are usually a few millimeters to several centimeters in height, rendering them inconspicuous and easily overlooked. They are normally associated with moist and shaded environment, but a few species can tolerate a wide range of harsh environments, e.g. alpine regions, deserts, and the Antarctic.

 

1.2              Importance of bryophytes

 

Bryophytes play an important role as pioneering plants in occupying primary habitats as well as secondary habitats after disturbance.  They serve as homes for many invertebrates, and are often found as construction material in bird nests.  Horticulturalists and landscape architects have found them invaluable, particularly the use of peat moss and in the construction of moss gardens and miniature gardens.  A few species are used in herbal medicine.  Johnson and Johnson has marketed a women’s diaper made with dried peat moss.  Bryophytes have also been used as air pollution indicators and as model system for research.

 

1.3              What are lichens (地衣)?

 

Lichens are symbiotic organisms composed of (a) an ascomycete or deuteromycete fungus and (b) a green alga or blue green alga. They form a mutually beneficial relationship, in which the alga provides nutrients for the fungus and the fungal tissue provides shelter for the alga. Morphologically, lichens could be classified into three categories in terms of life-forms: crustose, foliose, and fruticose.

 

Lichens prefer sunny and dry habitats, quite different from bryophytes which favor moist and shaded environments.

 

Lichens are important pioneering plants, and have been used as air pollution indicators, dyes, medicines, and foods.

 

1.4              How to distinguish bryophytes and lichens from other organisms?

 

 

Plant

Vascular bundle

Color

Nerve

Spore production in

Bryophytes

Leafy, or thallous

Absent

Generally green, same color on both dorsal and ventral sides

Present (single or two) or absent

Rounded or elongated capsule raised on a thin stalk (seta), or a needle-shaped sporangium

Lichens

Thallous

Absent

Colors other than green, different color on dorsal and ventral sides

Absent

Disc-like fruit bodies on the thallus

Small ferns and fern allies

Leafy

Present

Generally green, same color on both dorsal and ventral sides

Single

Sporaganium produced on the lower surface or margins of each fertile leaf or in cones

 

1.5              Main groups of bryophytes

 

 

Plant

Nerve (中肋)

Sporophyte

Color of capsule

Seta (蒴柄)

Capsule (孢蒴)

Hornworts

Thallous (not differentiated into stems and leaves)

Absent

Very strong, and lasting for several weeks

Green

Absent

Needle-shaped

Liverworts

Thallous or leafy (leaves arranged in two or three rows, and often lobed)

Absent

Delicate and short-lived, lasting several hours to a few days

Brown or black

Very delicate, translucent to transparent

Globose or ellipsoid

Mosses

Leafy (leaves arranged radially along a stem)

Present

Strong and long-lived, lasting several weeks

Green, brown, yellow or red

Strong, green, yellow or translucent

Various

 

1.6       Terms

 

Acuminate (漸尖的) ------ tapering to a long narrow point

Axillary hyaline nodule (腋透明節) ------ semispherical body formed by colorless cells in leaf axils

Crustose (殼狀的) ------ indicated lichens which form crusts that are so tightly attached to the rocks, trees, sidewalks, or soils they grow on that they can't be removed without damaging the substrate.

Dichotomous(二歧的) ------ regularly dividing into two roughly equal branches or parts

Distichous (兩列的) ------ arranged in two rows or ranks on opposite sides of stem

Foliose (葉狀的) ------ indicated lichens which are somewhat leaf-like, and they are relatively loosely attached to their substrates which they can be removed without damaging the substrate

Fruticose (枝狀的) ------ indicated lichens which they are usually round in cross section, and are branched frequently. They can be like little shrubs growing upward, or they can hang down in long strands.

Leafy (莖葉體的) ------ plants made up of regularly arranged leaves and stems.

Mucronate (短尖的) ------ ending abruptly in a short point

Radial (輻射狀的)------ arranged symmetrically in three or more rows around a central axis.

Subulate (鑽尖的) ------ shaped like an awl

Thallose (葉狀體的) ------ plants made up of flat or sheet of tissue, with no differentiation of stems and leaves.

Undulate (波紋狀的) ------ wavy



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