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I know how to apply anatomical directional terms (e.g., dorsal/ventral, anterior/posterior, etc.) for animals as a whole (bipeds and quadrupeds).

Recently, I've been studying plant physiology, and I came to know that the upper surface of a leaf is the ventral surface and the lower surface of the leaf is the dorsal surface. I cannot understand how these terms are applied to plants and leaves.

I've also seen anatomical directional terms being used for body organs such as the brain.

I want to know how anatomical terms are applied for parts of plants and body organs.

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    $\begingroup$ Wonderful question. Yes in biology there are various terms to indicate directionality and frame-of-reference for a phenomenon (such as transport) or a picture (eg. a section) $\endgroup$ – Always Confused Feb 4 '17 at 19:22
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First, for reference, see here for a discussion about the difference in directional terms between bipeds and quadrupeds as well as a fairly complete explanation of word meanings/etymology.

  • The etymological meanings of the various anatomical directional terms should help explain their usage in body organs. For example:

    Ventral -> "belly" side
    Dorsal -> "back" side
    Anterior -> "before" or "toward the front"
    Posterior -> "after" or coming after (opposite to) the anterior 
    

For body organs (or other body parts):

This SE question addresses hands and feet, while this page from Bryn Mawr College directly demonstrates the usage of anatomical positional terms of the brain:

brain anatomical positions

Rostral/ Anterior --->   Head or front end
Caudal/ Posterior --->  Tail or hind end
Dorsal  --->    Back or top side
Ventral --->    Belly or bottom side

Anatomical positional terminology for brains is consistent across organisms. Here is another picture demonstrating anatomical positional terminology of this organ from Santa Monica college:

brain anatomical positions


For plants, see "Plant Identification Terminology: An Illustrated Glossary" (Harris & Harris, 2001):

Dorsal. Pertaining to the back or outward surface of an organ in relation to the axis, as in the lower surface of a leaf; abaxial. Figure 407.

Ventral. Pertaining to the front or inward surface of an organ in relation to the axis, as in the upper surface of a leaf; adaxial. Figure 1428.

Ventral/Dorsal in plants

Therefore, dorsal/ventral are determined relative to the axis of where the leaf connects to the stem (ie., the axil). Because of this, in my experience terms such as abaxial and adaxial would be preferred when referring to plants.

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  • $\begingroup$ So, back and bottom are opposite terms. Aren't they? $\endgroup$ – MrAP Feb 3 '17 at 18:59
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    $\begingroup$ @MrAP well that depends on which context you're talking about. In some instances (e.g., quadrupeds) they are opposite and in other instances (e.g., bipedal anatomy) they are orthogonal. In plants, neither appears to be the case b/c from a whole plant perspective, "back" and "bottom" would be synonymous when referring to a leaf. However, just like when we refer to the dorsum of a human foot, using dorsal (i.e., "back") when referring to a leaf uses a different point of reference (POR) than the whole plant -- dorsal still means "back", but in the case of a leaf, the POR is the leaf axil. $\endgroup$ – theforestecologist Feb 3 '17 at 19:08
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    $\begingroup$ This is why word etymology is so important. :p $\endgroup$ – theforestecologist Feb 3 '17 at 19:10
  • $\begingroup$ So, ventral refers to the belly side and dorsal refers to the side opposite to the belly side which is always the back side but ventral may not always be the bottom side. Right? $\endgroup$ – MrAP Feb 6 '17 at 19:55
  • $\begingroup$ So, overall, the trick to understanding all of this is threefold. First, understand that each of these words has etymological meaning/background -- e.g., "ventral" originated from terminology referring to the belly side and "dorsal" originated from terminology referring to the "back." The second part of these concepts is understanding that these terms are applied in different fashions (i.e., using different points of reference). Further this is not always done appropriately based on the etymological meaning of the words themselves... $\endgroup$ – theforestecologist Feb 7 '17 at 21:35
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Dorsal and Ventral is very much confusing term as well as very casual term (and unscientific enough... Because we cannot compare our ventre or front with plants'). Unfortunately this casual terms widely used.

I usually avoid the term "dorsal" / "ventral" and "upper" / "lower" since there are available and better synonym Adaxial and Abaxial.

ADAXIAL SURFACE AND ABAXIAL SURFACE OF LEAF

Fig-1. Adaxial and abaxial surfaces of leaf shown on the same leaf-drawing provided in another answer.


P.S.

The term "dorsal" and "ventral" have another (quite opposite) usage in case of thalloid bryophytes such as Riccia and Anthoceros. and there are also use of terms "upper" and "lower" surface; in case of those bryophyte thalli; "ventral" or front-side is the "lower" side (towards ground) ; and "dorsal" or back-side means the "upper" side.... and that is exactly opposite of leaves' terminology.

example: Diagram from the textbook, College Botany , Vol-2, by Ganguly & Kar, New Central Book Agency...

Riccia Surface

The diagram (its Fig. C) describes the lower (ground-touching), rhizoid-containing surface as Ventral surface.

Diagram from another textbook, Botany for degree-students- bryophyta, by B.R. Vashishta, A.K Sinha and Adarsh Kumar; S-chand publications

VS through thallus

The side where "dorsal groove" has been pointed; is its upper surface.

$$\begin{array}{c|c|c}\hline \bbox[coral]{\textbf{term}} & \bbox[yellowgreen]{\textbf{usage in an angiosperm leaf}} & \bbox[yellowgreen]{\textbf{usage in thalloid bryophyte}}\\\hline \text{VENTRAL} & \text{Upper side, Adaxial side}& \text{Lower side}\\\hline \text{DORSAL} & \text{Lower side, Abaxial side}& \text{Upper side}\\\hline \end{array}$$

So a thalloid bryophyte's "dorsal" or "back" (which is upward) side is not comparable to an angiosperm leaf's "dorsal" or "back" (which is downward) (best to say "abaxial") side.

Similarly a thalloid bryophytes "ventral" or "front" (which is lower or ground-touching) side is not comparable with an angiosperm leaf's "ventral" or front" (which is upward) (better to say adaxial) side.

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