Advanced Twig Anatomy: Everyone Needs Buds (Part II)

Size: px

Start display at page:

Download "Advanced Twig Anatomy: Everyone Needs Buds (Part II)"

Timothy Gallagher
6 years ago
Views:

continuing education unit Advanced Twig Anatomy: Everyone Needs Buds (Part II) By Objectives Describe various parts and tissues in and on hardwood twigs Explain the relationships between different

1 continuing education unit Advanced Twig Anatomy: Everyone Needs Buds (Part II) By Objectives Describe various parts and tissues in and on hardwood twigs Explain the relationships between different twig attributes and identification Define awareness of botanical terminology used in angiosperm twig anatomy Assist professionals in understanding the language used in tree identification keys Use select twig attributes to identify several common tree genera CEUs for this article apply to Certified Arborist, Utility Specialist, Municipal Specialist, Tree/Worker Climber, Aerial Lift, and the BCMA science category. W What Are Buds? A noticeable feature of a twig is its buds. Buds are compound protective devices used to shield growing points during non-growth periods. Buds can be composed of a growing point, developing tissues (leaves, flowers, or both), unexpanded primordial internodes, compacted primordial nodes, additional primordial lateral growing points, and bud scales (waxed paper-like coverings). Bud scales (cataphylls) are modified leaves or immature bracts that cover all or part of a growing point and associated tissues. Buds are usually described by their position. Bud positions include terminal buds (at tip of twig) and pseudoterminal buds [the most apical axillary bud beside a terminal twig scar (improperly called a terminal branch scar)]. Terminal bud abortion and generation of a pseudoterminal bud, or false terminal bud, can generate a zigzag appearance in twigs and branchlets. More Bud Positions Other bud positions include axillary, extra-axillary, and accessory. Axillary buds (also called suppressed or lateral buds) are located at the base of a leaf in a leaf axil (on a twig in the area between the twig surface and leaf base). Figure 1. An idealized cross-sectional view of a terminal vegetative bud at the end of a twig. Extra-axillary buds are formed anywhere else but in a leaf axil or in a terminal position. Accessory buds are extra buds clustered around an axillary bud within the same node (nodal torus). Accessory buds can be found in two forms: a superposed accessory bud position occurs just above or below an axillary bud, and a collateral accessory bud position occurs to either side of an axillary bud. Bud Features Buds vary in how they are held on a twig on the surface, sunken or submerged, or held up on a pedestal or peg. Buds can appear to be tightly grown against a twig surface (appressed) or more loose or open. There are a number of descriptive bud shapes ranging along gradients: round end to pointed end; long to short; narrow (thin) to wide (fat); cone to oval to round overall shape; and, stalked base to sessile base. Naked growing points (sometimes called naked buds) are without protective scales but can be covered with primordial leaves and trichomes. 12 Arborist News

Figure 2. General accessory bud locations within the same nodal torus. Twig Scars For many tree specialists, tree identification concerns scar locations on a twig.

These visible scars represent former positions of twig structures, and include leaf, stipule, shoot, flower, or fruit scars.

2 Figure 2. General accessory bud locations within the same nodal torus. Twig Scars For many tree specialists, tree identification concerns scar locations on a twig. A scar is a visible periderm disruption after abscission or removal of an organ. These visible scars represent former positions of twig structures, and include leaf, stipule, shoot, flower, or fruit scars. General types of twig scars would include leaf scars, inflorescence scars, stipule scars, bud scars, and terminal bud scars. As any twig part dies or falls off, residual disruption in periderm appearance says a lot about past anatomical positions. Bud Scale Attributes Scale number Naked (no scales) Single scale (one scale) Valvate scales (two non-overlapping) Two ranked scales (opposite overlapping) Imbricate scales (alternating overlapping) Scale surface Smooth Tricombes (plant hairs) Striate (distinct lines / ridges) Scale edge Entire (smooth) Fringed (fimbriate) Leaf Scar Leaf scars remain visible on a twig when leaves fall. Leaf positions and scar position on a twig are divided into many types. Leaf scar position types include broad categories of alternate, opposite, and whorled. There are names and subcategories for specific leaf scar position types. The arrangement of scars show growing season leaf arrangement (alternate, opposite, subopposite, or whorled) and leaf position (raised or protruding petiole base, normal, Figure 3. Primary lateral (axillary) bud shape ranges. Scales On twig buds, covering bud scales occur in different forms, including absent (i.e., naked bud), a single scale covering, two ranked (paired overlapping scale covering), valvate scales (two non-overlapping scales), or imbricate scales (several alternating and overlapping scales). Bud scales can be smooth, covered with trichomes, or striate (with distinct lines or ridges). Bud scale edges are classified as entire (smooth) or fringed (fimbriate). Leaf scar position types A) Alternate one leaf scar per node (nodal torus). 1) Distichous alternate - leaf scars two-ranked. 2) Helical alternate a) Dextrose - leaf scars right hand spiral to tip. b) Sinistrorse - leaf scars left hand spiral to tip. B) Opposite two leaf scars per node (nodal torus). 1) Decussate opposite - leaf scars perpendicular to previous & next pair. 2) Distichous opposite - leaf scars aligned with previous & next pair (two ranked). 3) Spirodecussate opposite - leaf scars not perpendicular or in-line with previous and next pair. C) Subopposite two leaf scars per node (nodal torus), but each scar not exactly opposite the other. 1) Decussate subopposite - leaf scars perpendicular to previous & next pair of leaf scars. 2) Distichous subopposite - leaf scars aligned with previous & next pair of leaf scars (two ranked). 3) Spirodecussate subopposite - leaf scars not perpendicular or in-line with previous and next pair. D) Whorled three or more leaf scars per nodal torus. u april

continuing education unit of broken lines of vascular tissue that served a leaf.

Some bundle scars are valuable for tree species identification.

U-shape. Figure 4. Primary twig leaf scar location forms. or sunken/crater). There are a host of leaf petiole scars, which can be identified to genus or species, along with other scars.

3 continuing education unit of broken lines of vascular tissue that served a leaf. Bundle scars can be clearly visible, minute, not individually visible but can form visible lines, in clumps or groups, or not visible at all. Some bundle scars are valuable for tree species identification. Tree twig bundle scars most commonly present include: not visible (most species); obscured by surrounding tissue; 1 5 individual bundle scars; many minute bundle scars appearing as one; and a single U-shape. Figure 4. Primary twig leaf scar location forms. or sunken/crater). There are a host of leaf petiole scars, which can be identified to genus or species, along with other scars. Leaf-base scar shapes include thin crescent (falcate or sickleshaped), broad crescent, shield, half round, circular, oval, triangular, 3-lobed, heart, V-shape, U-shape, and horseshoe. Bundled Within each leaf-base scar are bundle scars (also called leaf traces in newly removed leaves). Bundle scars are remnants Figure 6. Half-round shaped leaf scars showing various types of visible bundle scars within. Stipules Some tree species have twigs with stipule scars. Stipule scars are visible periderm disruptions from where the stipules fell. Stipules are paired or single-fused growths on a twig from near the base of a leaf petiole, sessile leaf, or rachis. Stipules are modified leaves. Stipules vary in appearance by species and can be small leaf-like blades, bud scale-like growths, or spine-like points. They leave either a thin ring-like scar encircling (or partially encircling) a twig, or slit-like scars on a twig just above an axillary bud. Stipular scars are visible by mid-summer (usually in temperate trees). Figure 5. Twelve general tree twig leaf scar shapes. Bud Scars Periderm identification marks on twigs indicate the presence of a bud in the past, and its associated bud scales. Bud scars include terminal bud-scale scars or false terminal bud-scale scars, and axillary bud scars. A terminal bud-scale scar shows the position of last year s terminal bud location when extension growth began this year. A false terminal or pseudoterminal bud-scale scar shows the 14 Arborist News

A twig scar on a twig terminal (the old term for this was branch scar) is a visible periderm disruption of where a terminal internode (shoot module) was shed opposite across a twig from a false

4 position, opposite of a false terminal bud, where last year s terminal twig shoot died. This is also called a terminal twig scar. An axillary bud scar shows the position of an axil bud within a confluence area of a leaf and twig. A twig scar on a twig terminal (the old term for this was branch scar) is a visible periderm disruption of where a terminal internode (shoot module) was shed opposite across a twig from a false terminal bud. An axillary bud scar could be a single or multiple scars from accessory buds either superposed above or below the axillary bud position (superposed accessory buds), or collateral to either side of the axillary bud position (collateral accessory buds). Figure 8. Generalized views of true terminal bud & false terminal bud (pseudoterminal). Figure 7. Two primary stipule scar types, if present. Twigging Looking carefully at twigs is critical to understanding twig growth, applying proper tree health care, and for tree identification. Looking at twigs is similar to a physician reading vital signs. For example, twig length and diameter can suggest growth rate, while twig color can suggest additional health issues. Twigs allow a knowing person to read tree life and to make more accurate identifications. Here are the four most critical twig attributes used in tree genera (and species) identification: 1) evergreen, persistent, or, deciduous leaves; 2) leaf attachment scars opposite/whorled, or, alternate/clustered; 3) twig tip with true terminal bud, or, false terminal bud; and 4) bundle scars visible within leaf scars, or, no bundle scars clearly visible. Figure 9. Generalized views of true terminal bud scale scars & false terminal (pseudoterminal) bud scale scars. Four simple steps in identifying tree twigs STEP 1 = evergreen OR deciduous STEP 2 = opposite / whorled OR alternate / clustered leaf scars STEP 3 = true terminal bud OR no terminal bud / false terminal bud STEP 4 = individual bundle scars visible OR no bundle scars visible u april

continuing education unit Example Twig Features for Select Tree Genera Opposite leaf scars with terminal bud Acer = visible lenticels, three bundle scars Cornus = raised darkened leaf scars, leaf

at nodes, lenticellate, twigs stout, very small lateral buds, large leaf scars, circular bundle scar Catalpa = pith entire, small lateral buds, leaf scar three per node (whorled), stout twigs,

5 continuing education unit Example Twig Features for Select Tree Genera Opposite leaf scars with terminal bud Acer = visible lenticels, three bundle scars Cornus = raised darkened leaf scars, leaf scars joined by fine lines, three bundle scars Fraxinus = bud scales imbricate, bundle scars U-shaped Opposite leaf scars with no terminal bud Paulownia = pith chambered or excavated with solid pith at nodes, lenticellate, twigs stout, very small lateral buds, large leaf scars, circular bundle scar Catalpa = pith entire, small lateral buds, leaf scar three per node (whorled), stout twigs, crater-like leaf scars, circular bundle scars Alternate leaf scars with no clear bundle scars Robinia = no terminal bud, sunken lateral buds under leaf scars, paired spines, three-part leaf scars Maclura = no terminal bud, single unbranched slightly curved thorns, stipular scars, spur shoots Alternate leaf scars with terminal bud Ilex = 1 bundle scar, minute black stipular scars, lenticels visible, lateral buds often superposed, pith solid or spongy, 3 4 lateral bud scales (very difficult to identify to species using twigs alone) Alternate leaf scars with no terminal bud Celtis = 1 bundle scar, closely appressed lateral buds, zigzag form twig, pith chambered or diaphragmed in branchlets, single bud over single leaf scar Diospyros = 1 bundle scar, lateral buds closely appressed, laterals usually with two bud scales, buds solitary, pith diaphragmed, twig cross section round (terete), twig stiff Alternate leaf scars with 3 bundle scars Gleditsia = no terminal bud, forked thorns directly above node, raised lenticels, lateral buds partially sunken, lateral bud scales minute Juglans = terminal bud partially valvate, laterals superposed, twigs robust, pith cambered Alternate leaf scars with >4 bundle scars Quercus = terminal bud, pith angular in cross section, accessory buds clustered around terminal bud, lateral buds imbricate Carya = terminal buds much larger than lateral buds, no stipular scars, pith angular in cross section, pith solid or diaphragmed Platanus = no terminal bud, one wrinkled lateral bud scale, leaf scar surrounds bud (horseshoe shaped leaf scar), ring stipular scar around twig, zigzag form Figure 10. Key visible anatomy components on tree twig. Figure 11. Red maple (Acer rubrum) twig tips and axillary buds with leaf scar. Ron Lance; UGA Press Twig Presentation See Example Twig Features for a list of twig attributes for a few common tree genera. Figures 11 through 14 show example tree species drawings representing genera attributes, with the first four easy identification characters provided. Get to know twig features. Conclusions In trees, the first and newest aboveground elongation growth of a new year is shown by twigs. New growth is dependent upon vulgarities of past year s resource gathering, control, and efficient use, and this year s resource availability and environmental luck. Twigs mirror tree life 16 Arborist News

Figure 12. White ash (Fraxinus americana) twig tips. Ron Lance; UGA Press Figure 13. Catalpa ssp. twig tips (one with aborted terminal shoot still attached). Ron Lance; UGA Press and site quality.

Tree periderm: Less than bark deep. Arborist News 19(2):39 42. Coder, Kim D. 2012. Tree Anatomy: Twigs (Tree Anatomy Series).

Arborist News 23(1):12 18. Fink, S. 1983. The occurrence of adventitious and preventitious buds within the bark of some temperate and tropical trees. American Journal of Botany 70(4):533 542.

6 Figure 12. White ash (Fraxinus americana) twig tips. Ron Lance; UGA Press Figure 13. Catalpa ssp. twig tips (one with aborted terminal shoot still attached). Ron Lance; UGA Press and site quality. Tree health care providers should understand and use proper terms when discussing twigs. Arborists can learn many things from twigs! Additional Reading Coder, Kim D Tree periderm: Less than bark deep. Arborist News 19(2): Coder, Kim D Tree Anatomy: Twigs (Tree Anatomy Series). University of Georgia, Warnell School of Forestry & Natural Resources Outreach Publication WSFNR Coder, Kim D Advanced Twig Anatomy: Starting Little to Get Big (Part 1). Arborist News 23(1): Fink, S The occurrence of adventitious and preventitious buds within the bark of some temperate and tropical trees. American Journal of Botany 70(4): Harris, J.G., and M.W. Harris Plant Identification Terminology: An Illustrated Glossary (2nd edition). Spring Lake Publishing, Payson, Utah. Lance, R Woody Plants of the Southeastern United States: A Winter Guide. University of Georgia Press, Athens, GA. pp McSteen, P., and O. Leyser Shoot branching. Annual Review of Plant Biology 56: Figure 14. Honeylocust (Gleditsia triacanthos) twig, leaf scar, and thorn. Ron Lance; UGA Press u april

7 continuing education unit Rudall, P Anatomy of Flowering Plants (3rd edition). Cambridge University Press, New York. Schweingruber, F., A. Borner, and E.D. Schulze Atlas of Woody Plant Stems. Springer-Verlag, Berlin, Germany. Shigo, A.L Tree Anatomy. Shigo & Trees, Associates, Durham, New Hampshire., Ph.D., is a professor of tree biology and health care with the Warnell School of Forestry & Natural Resources, University of Georgia, Athens, Georgia, U.S. All diagrams courtesy of the author. All four twig drawings courtesy of the University of Georgia Press from Woody Plants of the Southeastern United States: A Winter Guide by Ron Lance (2004). Drawings used with written permission. CEU Questions Did you know that ISA members can take Arborist News quizzes online for free? Simply go online to the ISA web store ( log into your personal account, and select Online CEU Quizzes on the navigation bar on the left-hand side of the page. If you need a username and password, send us an (isa@isa-arbor.com). To receive one continuing education unit (1 CEU) for home study of this article, after you have read it, darken the appropriate circles on the answer form of the insert card in this issue of the magazine. A photocopy of the answer form is not acceptable. A passing score for this test requires sixteen correct answers. Please also complete the registration information on your answer form, including your certification number, and mail the form to: ISA, Certification, P.O. Box 3129, Champaign, Illinois, , U.S. Answer forms for this test, Advanced Twig Anatomy: Everyone Needs Buds (Part II), may be sent for the next twelve months. If you do not pass the quiz, ISA will send you a retake answer sheet. You may take the quiz as often as is necessary to pass. If you pass, you will not be notified; rather, you will see it credited on your CEU report (available online). Processing CEUs takes four to six weeks. CEUs for this article apply to Certified Arborist, Utility Specialist, Municipal Specialist, Tree Worker/Climber and Aerial Lift, and the BCMA science category. 1. Bud scales are a. immature leaves b. protective coverings c. a type of trichomes d. undeveloped stipules 2. Twigs that change direction of growth at each node (i.e., zigzag growth form) have a. damage from environmental stress b. false terminal buds c. nodal torus reversal d. terminal bud clusters 3. A twig with a false terminal bud would show a. a terminal twig scar b. straight internode elongation c. whorled bud scales d. all of the above 4. Whorled leaf scars at a single twig node represent past locations of a. alternate or clustered leaves b. spiral-arranged alternate leaves c. three or more clustered lenticels d. three or more leaves 5. A visible, naked growing point has a. a periderm covering b. many stipule scars c. no bud scales d. no primordial leaves 6. Buds are composed of all but a. compacted nodes b. growing points c. terminal scars d. unexpanded internodes 7. Axillary buds develop and are found a. at the base of leaves b. below branchlets and twigs c. on leaf margins d. to either side of thorns 8. A twig that had two leaves per node (nodal torus) would be considered a. alternate b. bifoliate c. opposite d. whorled 9. Common twig scars are derived from a. leaves b. stipules c. terminal buds d. all of the above 10. Stipules, if present, are modified from a. flower petals b. leaves c. scales d. thorns 11. Valvate buds can have a. a single scale b. alternating rows of scales c. two non-overlapping scales d. all of the above 12. Major components of twig appearance used for identification can include a. false axillary bud locations b. leaf scar positions c. number of diameter growth increments d. terminal bundle sheath size 18 Arborist News

mechanical injuries from other twigs 15. Leaf scar shapes represent a. branchlet shape b. petiole base cross section c. pith cross section d. specialized lenticel formation 16.

8 13. Buds can be a. located directly on twig surface b. supported by pedestals or pegs c. sunken into the periderm d. all of the above 14. An identifying twig scar represents periderm disruption from a. a location of a shed organ or tissue b. characteristic pest injury signs c. localized lenticel eruptions d. mechanical injuries from other twigs 15. Leaf scar shapes represent a. branchlet shape b. petiole base cross section c. pith cross section d. specialized lenticel formation 16. Accessory buds can be located a. around axillary buds b. beneath periderm c. on bundle scars d. randomly along internodes 17. A bud with a sessile base a. forms relatively tiny leaf scars b. is overgrown by periderm c. rises above the twig surface d. sits on the twig surface 18. Bundle scars within leaf scars represent a. exterior scar walls b. groups of leaf scars c. remains of large stomates d. remnant vascular connections 19. A terminal bud scale scar shows where the a. last axillary bud set developed b. newest twig bud base is positioned c. terminal bud is currently positioned d. terminal bud growth stopped last growing season 20. Stipule scars exist in two primary patterns a. longitudinal and slanted b. single and clustered c. slit and ring d. with and without bundle scars april

Advanced Twig Anatomy: Starting Little To Get Big (Part I) By Kim D. Coder

Advanced Twig Anatomy: Starting Little To Get Big (Part I) By Kim D. Coder Objectives Describe various parts and tissues in and on deciduous hardwood twigs Describe the relationships between different