What is a Tree?

Tree Biology 2012 Tree History Question

What is the connection between this tree and the celestial body shown here? What is a Tree?

• Random House College Dictionary Definition: (1) a perennial plant having a permanent, woody, self- supporting main stem or trunk, ordinarily growing to considerable height and usually developing branches some distance from the ground; (2)any of various shrubs, bushes, and herbaceous plants, as the banana, resembling a tree in form and size. What is a Tree?

• Wikipedia: “A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance.[1] A minimum height specification at maturity is cited by some authors, varying from 3 m[2] to 6 m;[3] some authors set a minimum of 10 cm trunk diameter (30 cm girth).[4] Woody plants that do not meet these definitions by having multiple stems and/or small size are called shrubs. Compared with most other plants, trees are long-lived, some reaching several thousand years old and growing to up to 115 m (379 ft) high.[5]” What are the characteristics of a Tree?

• Their trunk is really a collection of overlapping leaf stalks

Are bananas, palms, and tree ferns really trees trees?

http://www.sheilafinkelstein.com/PSE4/lesson1.html Are Grape Vines and Poison Ivy Trees? Do Trees form a Natural, Phylogenetic Group?

What is a natural/phylogenetic group? Do Trees form a Natural, Phylogenetic Group?

What is a natural/phylogenetic group?

Domain Kingdom Phylum/Division Class Order Family (aceae) Genus Species

*evolutionary groups supported by morphology, anatomy, genetics, molecular biology Prediction: If the woody trait is phylogenetically important, then all near relatives should all herbaceous or all woody.

Herbaceous Herbaceous

Woody Woody Woody Woody

Woody Woody Woody

Herbaceous Herbaceous Herbaceous Herbaceous Herbaceous Woody & Herbaceous Relationships Is the woodiness phylogenetically meaningful?

Fabaceae--legumes Clover, alfalfa, bird’s foot trefoil, sweet pea, and beans are herbaceous legumes. Redbud, black locust, Kentucky coffee tree, and honey locust are woody legumes. Woody & Herbaceous Relationships Is the woodiness phylogenetically meaningful?

http://www.networlddirectory.com/images/blogs/8-2006/strawberry-flowers-51270.jpg

Rosaceae Strawberries (herbaceous) and apple trees are related through a common ancestor. Woody & Herbaceous Relationships Is the woodiness phylogenetically meaningful?

Order Lamiales Mints, snapdragons, foxgloves, and Salvia are herbaceous members. Woody & Herbaceous Relationships Is the woodiness phylogenetically meaningful?

Order Lamiales

. . . But ash trees and catalpa are also members. Woody & Herbaceous Relationships Is the woodiness phylogenetically meaningful?

Mustards (Brassica) Maples (Acer) and Basswoods are herbaceous. (Tilia) are woody trees.

Order Malvales of Eurosids II Woody and Herbaceous Plants can Be Found in the Same Genus

Asteraceae Examples of Woody Distribution Among Seed Plants Red = tree; Green = herbaceous

Gymnosperms

Carnations Barberry Core Eudicots

Geranium Eucalyptus Strawberry, Cherry, Apple Peas, Black Locust Eurosids I Seed Plants

Mustards Cotton, Basswood Eurosids II Maple

Flowering Plants or Angiosperms Dogwoods Rhododendrons Tomato & relatives Asterids Mints, Ash, Catalpa Marigold, Daisy, Sunflower Trees are sprinkled throughout many different lineages of flowering plants.

Therefore the “woody” condition is not the result of inheritance through a single common ancestor.

Polyphyletic

Trees are an excellent example of CONVERGENT EVOLUTION

—evolution of similar traits because of similar environmental conditions. Ecological Consequences of Being a Tree (i.e., a tall woody plant that is long-lived and self-supported)

• Many years to reproduction

• Increased reproduction by producing flowers on many stems

• Great life time reproduction by producing flowers over many decades

Ecological Consequences of Being a Tree (i.e., a tall woody plant that is long-lived and self-supported)

• Modify local environment – Soil temperature – Air temperature – Humidity – Soil moisture – Light – Diverse micro-niches • Organism depending on these altered conditions – Fungi, amphibians, birds, insects, spring ephemerals, ferns, mosses, other trees

Ecological Consequences of Being a Tree (i.e., a tall woody plant that is long-lived and self-supported)

• High energetic cost to producing more wood and maintain it

• Accumulation of biomass and carbon

• Susceptibility to wind

• Live in ecologically stable environments and cope with periodic stress Evolutionary Consequences of Being a Tree

• Multiple growth points and • Evolution tends to be mutation—genetic diversity slower in woody plants (7- within trees 15x slower rate of evolution • Multiple mechanisms to than herbs) increase mating between • Lower Diversification trees (outcrossing) • Greater chromosome • Woody plants maintain numbers (13.1 for woody more genetic variation than plants, 9.3 for herbs) herbaceous plants • Generalize protection against organisms with short generation times Summary on Being a Tree

• Trees are polyphyletic

• Trees are long-lived and have high lifetime reproduction

• Trees have high levels of genetic variation

• Trees have slow rates of evolution and speciation