How large are the giant horsetails?



1.  Exceptionally robust giant horsetails (~4 cm diameter stems) in a most unlikely place (Arica, Chile)  
2.  David Attenborough with giant horsetails
3.  A report from Ecuador (early 1990's)
4.  A report from the early 1980's
5.  A report from Brazil (1926)
6.  10 cm diameter Equisetum stems near Orizaba, Mexico? (before 1900)
7.  Edouard André 's report from Ecuador (late 1800's)
8.  Richard Spruce's remarkable report from Ecuador (mid 19th century)
9.  Alexander von Humboldt's report

Other Equisetum species that can become "giants"


    In the past, both woody and herbaceous sphenopsids have reached large sizes, both in terms of aerial stem size and, probably, overall sporophyte size (i.e. the size of the whole interconnected network of rhizomes and aerial stems).  The largest horsetails were woody (i.e. produced secondary xylem1) and belonged to the genus Calamites (Calamitaceae).  The aerial stems of these plants sometimes attained heights of up to 30 m and diameters of up to 30 cm ( Scagel et al., 1984 ), although these stems were determinate in growth like those of modern horsetails (Eggert, 1962).  As in modern Equiseta, the clonal growth of Calamites via large underground rhizomes was probably indefinite and very extensive (Niklas, 1997).    Niklas (1997) stated that "using modern horsetails as a scale for gauging overall size, we can estimate that the sporophytes of Calamites may have been the largest organisms that ever lived."

was a genus of fossil horsetails that were possibly herbaceous and were very similar to modern Equisetum , belonging to the same family Equisetaceae.  In fact, there is some controversy as to whether Equisetites may actually have been congeneric with extant Equisetum ( Hauke, 1963 ). One of the largest Equisetites species, E. arenaceus , lived during the Upper Triassic period ( Kelber and van Konijnenburg-van Cittert, 1998 ).  This remarkable species had stems that averaged 25 cm in diameter and about 2.5-3.5 m in height  (Klaus-Peter Kelber, 2000, personal communication).  Stewart and Rothwell (1993 ) hypothesized that large Equisetites may have had secondary growth due to their size, but mentioned that there is no direct evidence for this.  Although there are no reports of living horsetails approaching the dimensions of these extinct forms, there have been several intriguing reports during the last 150 years of exceptionally large living Equiseta.

    Dr. Richard Hauke, in his 1963 monograph of Equisetum subgenus Hippochaete gave the following maximum stem dimensions for the giant horsetails, based upon his extensive study of herbarium specimens.

E. giganteum
E. myriochaetum
E. x schaffneri
Maximum stem height
5 m
8 m
4.5 m
Maximum stem diameter
2.4 cm
1.8 cm
2.2 cm

These dimensions indicate the giant horsetails are generally tall and thin.  The tallest stems generally are not self-supporting and rely on other vegetation for support.  However, there have been several compelling reports of giant horsetails reaching larger stem diameters than those reported by Dr. Hauke.  Below I describe these reports, starting with the most recent.  If you can provide any further information about these or other reports of unusually large giant horsetails, please contact me:

    I suspect that there is much genetic variability in the giant horsetails throughout their range.  Korpelainen and Kolkkala (1996 ) found that different populations within the species Equisetum arvense and E. hyemale in Europe where quite genetically distant.  This is probably due to the brief viability of Equisetum spores and the exacting conditions they require for successful development (see discussion of Ecology ), which would tend to curtail genetic exchange between populations.  Hence, I think that there may well be relatively isolated populations of exceptionally robust giant Equiseta that have not been noticed due to inadqueate sampling of the flora or inadequate observation of known populations. The fact that the remarkable Wollemi Pine (Wollemia nobilis), a true 'living fossil', was discovered not far from Sydney, Australia in 1994 suggests that major botanical discoveries remain a distinct possibility to this day.   Even in the extensively botanized land of Ireland a small population of a distinctive and robust variety (var. wilsoni ) of the normally diminuitive species E. variegatum was not discovered until the middle of the 19th century ( Newman, 1844 ; Page, 1997 ).  

    The first report below provides especially strong evidence of the existence of an isolated and remarkably robust living form of giant Equisetum:

Exceptionally robust giant horsetails (~3.5+ cm diameter stems) in a most unlikely place  
(A river valley in the Atacama desert of northern Chile)

    During the spring of 2001, I  had the good fortune to examine the most impressive Equisetum herbarium specimens I have ever seen.   These specimens, located at the Ohio State University Herbarium , were of E. giganteum from northern Chile (valleys of the Río Lluta,  Río Tana, and Río Camarones).  The specimens were large and very well-branched, the largest stem (from the Lluta valley) measuring ~2 cm in diameter.  When I checked the collection localities for these specimens (listed below), I was quite surprised to discover that they were found in an arid region, definitely not the sort of place one would expect to find such moisture loving plants.

    In the fall of 2001, I was delighted (and rather astonished) to discover beautiful photographs of a large colony of exceptionally robust E. giganteum growing in the Lluta Valley near the city of Arica in northern (photo of the Lluta Valley near Arica).  Dr. Thomas Schöpke, who took these remarkable photographs, reported that giant Equisetum are abundant along the roadside of highway 11 where it parallels the Lluta near Arica.  On the basis of close observation, he estimated that the largest stems were ~4 cm in diameter, and about 2.5 m tall.  Indeed, these plants appeared considerably more robust than any giant horsetails I had seen either in photographs or in person.  The tallest of these plants appeared to be self-supporting (i.e. not propped up by surrounding vegetation).

    Milde (1867 ) gave Arica as the type locality for Equisetum xylochaetum , a taxon which Hauke ( 1963 ) later subsumed under E. giganteum.  Hence, the presence of giant horsetails in the Arica region has been known for quite some time.  The herbarium specimens I examined conformed well to Hauke's description of E. giganteum (exhibiting square branch ridge tubercles and multiple bands of stomata in stem ridge valleys).  Marticorena and Rodríguez (1995 ) noted that E. giganteum in northern Chile are consistently larger (both in overall size and stem diameter) than plants from central Chile and suggest that plants from the two regions may constitute distinct taxa.

    I visited northern Chile for 10 day in December 2002 to observe these remarkable populations.  The widest stem I found, in the Tana Valley, was ~3.5 cm in diameter and the tallest stems were ~4-5 m high.  I brought back a voucher of the 3.5 cm stem, apparently making this the largest documented stem of a giant horsetail.  It is quite possible that the stems reach even larger diameters in northern Chile because I did not have sufficient time to thoroughly investigate many populations.

David Attenborough with giant horsetails

    I recently received a report that one of David Attenborough's TV programs included a segment showing him sitting beneath some very large giant horsetails.  According to the recollection of one person who saw the show, the plants were "as tall as small trees and thick as an arm".  Unfortunately, I do not have any information on the title of the program or where the plants were filmed.  If you have seen this program, please share with me any information you may have about it:

A report from Ecuador (early 1990's)

    A friend of mine, who is a keen pteridophyte enthusiast, believes that he saw some very robust giant horsetails while visiting Ecuador in the early 1990's.  He believes that the plants may have been more than 4 cm in diameter.  The plants were along the road from Quito to Santo Domingo de los Colorades.  After hearing my friend's account, I corresponded about this observation with Dr. Calloway Dodson, an orchid specialist who lives in Ecuador.  Dr. Dodson mentioned that the largest horsetails he had seen in Ecuador where along the road above Tandapi (~2,000 m altitude) at km 35 from Quito to Santo Domingo (or km 65 from Santo Doming to Quito).  He stated that the plants are visible along an ~1 km stretch of road.  However, Dr. Dodson did not  think that he had seen plants over ~2.5 cm in diameter.  It should be easy for someone visiting or living in Ecuador to check the actual maximum diameters (and heights) of the plants in the populations along the road between Quito and Santo Domingo..  

(For another report of exceptionally large Equisetum in Ecuador, please read the last discussion on this page ( Richard Spruce's account )).

A report from the early 1980's

    In the "Atlas of Medicinal Plants of Middle America" (1981) by Dr. Julia Frances Morton, there is an entry fo Equisetum giganteum.  Dr. Morton describes this species as having a "green, hollow main stem to 4 cm thick and 9 m high".  Unfortunately, no reference is given for these maximum size estimates.  The only locality mentioned in the entry is Venezuela:  "Great armloads of the fresh plant are brought into the markets of Valencia, Barquisimeto and Maracaibo (Venezuela)".  There is no indication of whether the maximum size estimates may be based upon Venezuelan plants.

A report from Brazil (1926)

    Correa (1926) reported in "Diccionario das Plantas Uteis do Brasil", Vol. 2, p. 158, that Equisetum giganteum in Matto Grosso, Minas Gerais, and Amazonas States of Brazil as being arborescent, erect, and reaching 9 m in height (though no diameter was given).  The exact quotation is "caule arborescente, até 9 metros de altura, erecto".

10 cm diameter Equisetum stems near Orizaba, Mexico? (before 1900)

    About two years ago, while perusing botany texts from the early years of the 20th century, I found remarkable reports of a giant horsetail, Equisetum schaffneri, reaching a diameter of 10 cm (and a height of 2 m) in Mexico.  These reports intrigued me a great deal because I had not read about this exceptional plant in later sources.  Upon closer examination, I discovered that the apparent source of these accounts was a chapter on Equisetum by the German botanist Sadebeck ( 1900 ) in "Die Natürlichen Pflanzenfamilien".   In this chapter, Sadebeck states that E. schafferni reaches 10 cm but has a large central hollow:

Stems reaching 2 m in high and diameter approximately 10 cm, but because of the quite coarse central cavity not very robust. Differs from all under A. named species by protrusive teeths on the striae of the branches. Mexico (only at (or near) the place Orizaba), Peru, Chile. 

(Translation from the original German courtesy of Dr. Michael Matus.  A scanned image of the original german passage is also available.)

    I corresponded with Dr. Richard Hauke, author of the standard monographs of the genus Equisetum (Hauke, 1963 ; 1978 ) about this report.  Dr. Hauke had been aware of this report, but had assumed that Sadebeck had made an error and actually intended to state that the diameter was 1.0 cm.  To investigate this possibility, I compared the giant horsetail measurements given in Sadebeck ( 1900 ) with those in Milde ( 1867 ) for the 7 giant horsetail species they recognized:

Sadebeck (1900)

Milde (1867) 1

height (m)
diameter (cm)
height (m)
diameter (cm)
E. giganteum
E. martii    
E. mexicanum
E. myriochaetum
E. pyramidale
1.216 m
0.735 - 1.05
E. Schaffneri
1.824 m
E. xylochaetum
1.5- 2
3.04 m

1.  Milde's original measurments were converted to metric units from an earlier system of units.  Many thanks to Dr. Michael Matus for providing the necessary conversion factors.

    On the whole, Sadebeck's and Milde's estimates tend to correspond reasonably well, except for E. schaffneri . Interestingly, Milde gives 1.05 cm for the diameter of E. Schaffneri .  Furthermore, both Milde and Sadebeck give Orizaba as the most precise location (probably the type locality) for E. Schaffneri .

    However, Sadebeck's statement above suggests he did realize that the diameter he was reporting was unusually large.   Indeed, Sadebeck qualified his statement of the diameter with the words "but because of the quite coarse central cavity not very robust."  Hence, it seems possible that he had a source for this diameter that he considered reliable.  He may have examined an herbarium specimen or found the description in another source.  An examination of European herbarium specimens that Sadebeck examined might prove fruitful.

    Dr. Hauke (personal communication, 2000) made a good point about the likely biomechanical problems of a 10 cm thick herbaceous stem with a large central cavity.  It would seem that such a stem or rhizome would not be strong enough to push through soil (with the exception, perhaps, of very soft mud) and aerial stems might have little capacity to support themselves.  However, certain bamboos have hollow stems and rhizomes 10 cm in diameter, yet lack secondary growth (McClure, 1966 ).  Bamboos achieve these large sizes through extensive lignification (Judziewicz et al., 1999 ).  Although Spatz et al.( 1998 ) did not find positive evidence of lignification in the supporting tissues of the E. giganteum? (identification uncertain) stems they examined, Speck et al. ( 1998 ) found slight lignification in supporting tissues of E. hyemale .  The extinct species Equisetites areanceus , a close relative of Equisetum that lived during the Upper Triassic ( Kelber and van Konijnenburg-van Cittert, 1998 ), had stems (possibly herbaceous) that reached 25 cm thick and perhaps 2.5-3.5 m tall  (Klaus-Peter Kelber, 2000, personal communication). However, Seward ( 1898 ) mentioned interesting indirect evidence that E. areanceus had secondary growth.  I do not know whether Equisetites arenaceus stems had large central cavities.  Hence, the biomechanical limitations on stem size in herbaceous horsetails remain uncertain.

    However, the possibility that there may have been some basis to Sadebeck's report suggests that it might be worthwhile to investigate the vicinity of Orizaba, Mexico for unusually large Equisetum.  If such exceptionally large plants exist, it would seem likely that the locals in the Orizaba area would be aware of them .

Edouard André's report from Ecuador (late 1800's)

  Edouard André , a landscape architect and horticulturist, visited Ecuador during an expedition to South America that began in 1875.  Upon his return to Europe, he wrote the book "L'Amerique Equinoxiale" ( 1883 ) about his travels, wherein he described " Equisetum forests" in the valley of Río Pilaton near Quebrada Calulu (on the southern side of the valley ~1/3 of the distance from Tandapi to Río Napa) (location information courtesy of Benjamin Øllgaard).  Accompanying André's description is a remarkable illustration of men riding on horsback through a swamp dominated by immense (tree-size) horsetails towering above the riders (This illustration is reproduced in Moyroud ( 1991 ) and Moran (2000 )).

    I have corresponded with Dr. Benjamin Øllgaard about André's illustration.  Dr. Øllgaard is a Professor at Aarhus University in Denmark who has worked extensively with Lycopodiaceae in Ecuador and has also observed giant Equiseta in Ecuador . Dr. Øllgaard told me that the Andre's text mentions "forests" of giant horsetails exceeding 5-meters high, but does not say anything about stem diameter. Hence, André does not provide many details about the size or form of the plants he saw.  Professor  Øllgaard observed that the illustration was apparently made by an artist working for the publisher who likely let his imagination "run wild" when preparing the illustration.  André's actual description of "Equisetum forests" with plants exceeding 5 m tall corresponds to what professor Øllgaard has observed during his extensive fieldwork in Ecuador.  However, Dr. Øllgaard has informed me that, although giant Equiseta are relatively common in Ecuador, he has not seen any with stems thicker than ~2.5 cm.  However, he has observed that when 2.5 cm thick stems are flattened in herbarium presses, they can become ~4 cm wide.

Richard Spruce's remarkable report from Ecuador (mid 19th century)

    Richard Spruce undertook a long expedition to study the plants of tropical South America during the 1850's and early 1860's.  During that time he kept a journal and correspondence which were later edited and published by his friend, the famous naturalist Alfred Russell Wallace ( Spruce, 1908 ).  Contained in Spruce's published journal are some observations of a remarkable stand of giant Equisetum along the Río Pastaza in Ecuador.  I quote these passages on the main page of this website.  Spruce's observations seem quite compelling because he was an extremely knowledgeable and careful botanist.  His description of stems "nearly as thick as the wrist at the base" suggests that the plants he saw were exceptionally robust (perhaps 4 cm thick or larger).  Spruce's journal account indicates that the giant plants were found on a plain along the Río Pastaza between its confluences with the Río Topo (Río Toro on my modern map of Ecuador)and Río Verde (although the site was probably closer to the Topo).  This stretch of river is approximately 10 km long and is located in an area with an  altitude range of 1200-2000m, which is consistent with the known altitude preferences of the giant horsetails.  It would probably not be difficult to check whether any unusually large Equiseta still inhabit this area, especially since a road parallels this stretch of river.

Alexander von Humboldt's report

    I have heard that Alexander von Humboldt, the famous German explorer and naturalist, mentioned seeing 27 foot (~8.2 m) tall Equisetum, presumably during his explorations in the Americas (1799-1805).  Unfortunately, I do not know where Humboldt mentioned giant Equisetum in his writings.  I would be most grateful for any additional information on this report.

Other Equisetum species that can become "giants"

    Equisetum telmateia is the largest member of the subgenus Equisetum .  This densely-branched species, which is native to Europe and the Pacific Coast of North America, is winter deciduous.  Under favorable conditions (protected situations under light shade) in the British Isles, it can reach 2.5 m in height and 3 cm or more in diameter (Page, 1997 ).  However, this species has relatively succulent stems in contrast to the hard and fibrous stems of the giant horsetails of the subgenus Hippochaete.

    The Irish botanist Robert Lloyd Praeger ( 1951 ) reported on a remarkable specimen of Equisetum robustum (considered by Hauke ( 1963 ) to be a synonym for E. hyemale var. affine ), originally from North America, attaining a height of 15 feet (4.57 m) in a cool greenhouse in Manchester.


1.  Interestingly, the vascular cambium of Calamiteswas unifacial (i.e. produced secondary xylem towards the stem center, but not secondary phloem) (Eggert, 1962) like that of the woody arborescent lycopod Lepidodendron (Eggert, 1961).  This contrasts with the bifacial cambia of modern woody gymnosperms and angiosperms that produce both secondary xylem towards the stem center and secondary phloem towards the outside of the stem.

If you have any comments or questions, please contact the author, Chad Husby ( or )

© Chad E. Husby 2003

Last modified March 19, 2003


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