The ‘Nodding’ of Heads of Chaptalia texana

by Bob Harms 

‘Nodding’

The species was known to Carl Linnaeus already in the 18^th century, and it was Linnaeus who assigned the specific epithet 'nutans' in his Syst. Nat. ed. X, 2:1214, 1759, where the total identifying description of the species (under the genus Tussilago) was:

T. scapo unifloro ebracteato, flor. nutante [with nodding flower], fol. lyratis apice obtusis.

In his 1944 treatment of C. nutans A. Burkart notes ("Estudio del género de compuestas Chaptalia." Darwiniana 6:565):

Extracts from Burkart's drawings for C. nutans and C. nutans var. texana are shown below.

C. nutans, Burkart, Fig. 12	C. nutans var. texana, Burkart, Fig. 13
Drawings extracted (and colorized) from Burkart 1944

While the bud [red] is clearly pendent, the slightly tilted heads shown at (presumed) anthesis are not bent downward, and do not seem likely to have qualified as ‘nodding’ for 18^th Century botanists, who apparently took such terms seriously. For example, James Lee 1776 (An introduction to the science of botany, p. 493) list distinct terms appropriate for the orientation of the peduncle, including:

R. J. Thornton, A Grammar of Botany, 1818, provided more clarification:

The Oxford English Dictionary recognizes the special botanical usage of ‘nodding’:

The Glossary of D. S. Correll & M. C. Johnston, Manual of the Vascular Plants of Texas (1970) provides somewhat similar definitions, but doesn't maintain the earlier distinctions:

The Oxford English Dictionary also provides nonbotanical definitions for nod which might seem to be the basis for some of the confusion; e.g., for the verb:

More Recent Descriptions

1. Correll & Johnston 1970 describe the head of C. nutans (incl. C. nutans var. texana) as:
   head nodding, 12-25 mm. high, with about 150 flowers;

2. In a concise treatment of C. nutans (incl. C. nutans var. texana) B. Simpson provides significant additional detail to the nodding behavior, associating it with stage of development, and includes it both in her key and in the descriptive text ("Chaptalia," Flora of Panama; Annals of the Missouri Botanical Garden 62:1278-1280, 1975):
   a. Scape bractless; leaves lyrate; heads nodding when young and at fruit maturity ..... C. nutans

   The species may be recognized by the orientation of the heads; when immature or as the achenes are shed they are nodding but at anthesis they are upright.

   But Fig. 102 (p. 1279) [below left] doesn't seem to clearly show this behavior. The two taller scapes on the left seem typical of the peduncle/head orientation at dispersal, neither are directed downward – the taller of the two is quite erect, more so than the heads at anthesis. [Compare with C. texana with fresh material.]

   C. nutans, Simpson, Fig. 102	C. nutans, Nesom, Fig. 7	C. texana, Nesom, Fig. 8
   Drawings extracted (and colorized) from Simpson 1975 & Nesom 1995

3. In his most recent treatment of C. texana (Asteraceae, Flora of North America, Vol. 19, 20 & 21) G. L. Nesom also uses nodding habit to distinguish C. texana, with language very similar to Simpson's description of C. nutans.
   Heads nodding in bud and fruit, erect in flowering; ....

   And Nesom 1995 (Revision of Chaptalia (Asteraceae: Mutisieae) from North America and continental Central America. Phytologia 78:153–188) presents drawings said to show the habit of the two species, extracted above. The C. nutans bud [red] does indeed meet the above conditions for ‘nutans’, but the dispersal stage [left] head of C. texana] is quite rigidly erect.

4. In sharp contrast with Nesom's description stands that in W. F. Mahler, Shinners' manual of the North Central Texas flora (Botanical Research Institute of Texas, 1988; p. 335):
   heads solitary, with ca. 150 flowers, nodding in flower, erect in fruit;
   But the book presents the very same drawing as Nesom's Fig. 8 (above)!

Ten Blind Men and the Elephant

So how am I to make sense out of this? For starters, my experience has been limited to C. texana in Texas, with the 40 pressed specimens in the TEX & LL herbaria plus intensive contact with 4 different populations in Central Texas (as illustrated and documented on this website). But since I have no knowledge of C. nutans other than what is in the literature (noted above), my discussion is limited to C. texana.

My inspection of the TEX/LL Herbaria specimens tells me that evidence for habit is not to be found in these mounted specimens. One exception was a specimen from Val Verde County with a sharply drooping head (!cernuous), with a peduncle twist of greater than 180°:


24 Nov. 1984, B. Ertter et al 5516 (TEX)

In terms of nodding behavior I have documented two distinct forms:

1. open head (head not bent downward at bloom; my type I)
2. closed head (head bending downward at bloom; i.e., my types II, III, IV & II–III).

A comparison of Nesom, Mahler, and my two forms is given in the following table:

	bud	flower	dispersal
Nesom	nodding	erect	nodding
Mahler	?	nodding	erect
open head	nodding	±erect	±erect (may also bend slightly downward)
closed head	nodding	nodding (early) to cernuous (late)	±erect

Neither Nesom nor Mahler match my observed type I, although Mahler does match my 'other' types (assuming buds as nodding).

If the blind wise men and the elephant metaphor is appropriate, we know who the blind men are, but what is the elephant? In my opinion some of the differences may stem from loosely applied non-technical terminology. As noted above the use of ‘nodding’ to describe the peduncle–head alignment does not seem to be the same for all observers, or even for the different stages of development by the same observer. And while all would probably agree that a small undeveloped head represents a 'bud,' the development from early anthesis to dispersal doesn't yield clearly defined steps without additional qualification. I have found it necessary to recognize six stages of peduncle/head orientation to describe adequately what is going on; see:

• Nodding Patterns with Open–Heads: Type I
• Nodding Patterns with Closed–Heads: Type II
• From Bud to Dispersal for the Same Head

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