Plant Morphology (Root) Weerachon Sawangproh, M.Sc. (Environmental Science)

Learning Objectives Students are able to describe external structure of root Students are able to describe several roots that are modified to perform unusual functions

Outline of Study Kinds of root systems Root functions Modified roots

Root structure Taproot system or primary root system 2. Fibrous root system 3. Adventitious Roots

1. Taproot system Emerge from the radicle (of seed) In most dicots: the radicle enlarge to form a taproot that persists throughout the life of the plant with many smaller branch (lateral) roots

The type of root system consisting of a large taproot and smaller branch roots is called a taproot system

Shapes of taproots Conical Napiform/ Turbinate Fusiform

Conical shape: broad at the base and tapering gradually towards the apex e.g. carrot and dandelion

Napiform/ Turbinate shape: very broad at the base and tapers suddenly like a tail at the apex e.g. turnip turnip radish มันแกว

Fusiform shape: swollen in the middle and tapers towards the base and the apex e.g. radish

2. Fibrous root system Most monocots: a fibrous root system consisting of an extensive mass of similarly sized roots the radicle is short-lived

Fibrous root system Tuberous roots: look like tubers, but are swollen, nutrient-storing fibrous root Fascicled root/ root tuber: swollen fibrous root that can have buds to produce new shoots, so this is a form of cloning

รากมันเทศ มันมือเสือ รากปทุมมา Tuberous root รากมันเทศ มันมือเสือ รากปทุมมา

Fascicled root รากกระชาย รากรักเร่ รากต้อยติ่ง

3. Adventitious roots Roots that form on organs other than roots Adventitious roots of most monocots begin growing soon after the seed germinates

Primary functions of root Anchorage – locating water and minerals Storage – storing large amounts of energy reserves e.g. carrot and sugar beet Absorption – absorbing large amounts of water and dissolved minerals Conduction – transporting water and dissolved nutrients to and from the shoot

Modified Roots Storage root Reproductive root Nodal roots Aerial roots/ Pneumatophores Prop or stilt roots Buttress or tabular roots Contractile roots Haustorial/ parasitic root Climbing roots Photosynthetic root

Storage root Storing starch e.g. beets, turnips, radish, dandelion, carrot, and cassava Storing sugar e.g. sweet potato Storing water e.g. dessert plants

Reproductive root produce adventitious buds called suckers for reproduction

Nodal roots (a type of mutualism in the roots of legumes) - cortical cells of the root infected with Rhizobium causing swellings called nodules

Aerial roots/ Aeration root - roots that are formed in and exposed to air e.g. by epiphytes and coastal swamp trees such as mangroves Aerial roots have special air channels (lenticels) for gas exchange in the atmosphere

Aerial root of Banyan tree Aerial root of bonsai

The root of mangrove trees called pneumatophores that import oxygen from the atmosphere Pneumatophores contain as much as 80 % aerenchyma

Prop or stilt roots - adventitious roots that develop on a trunk that grow into a substrate to provide mechanical support

Buttress or tabular roots: vertically flattened roots that project out of the ground and lower trunk at the base of large trees to resist uprooting of large tropical trees

Contractile roots – root that pull a plant into the deeper soil, commonly found on corm and bulb-forming plants e.g. lily and Gladiolus, as well as on other plants e.g. ginseng and dandelion

Haustorial/ Parasitic root - roots that parasitize (intrude) other plants (the tissues of the host)

Mycorrhizal roots - the association between a root epidermis/ cortex and a fungus are called mycorrhizae (a type of mutualism) e.g. orchid and maple

Climbing root - roots that develop from the stems of certain climbing plants e.g. ivy to serve the attachment to its support

Velamen is a site of water storage Photosynthetic root - roots that are flat and green serving as the photosynthetic site

Summary Most roots have a variety of functions, including anchorage, absorption, and hormone production Other roots may be specialized for other functions

References Moore, R., Clark, W. D., Stern, K. R. 1995. Botany. Wm. C. Brown Publishers, U.S.A. 824 pp. Plant Structures: Stems (online document: PDF file). Colorado State University Extension. 6 pp. available at http://cmg.colostate.edu/gardennotes/ (online: 10 July 2010)