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Anais da Academia Brasileira de Ciências (2019) 91(Suppl. 3): e20190396
(Annals of the Brazilian Academy of Sciences)
Printed version ISSN 0001-3765 / Online version ISSN 1678-2690
http://dx.doi.org/10.1590/0001-3765201920190396
www.scielo.br/aabc | www.fb.com/aabcjournal
An Acad Bras Cienc (2019) 91(Suppl. 3)
BIOLOGICAL SCIENCES
Are we close to knowing the plant diversity of the Amazon?
MICHAEL J.G. HOPKINS
Instituto Nacional de Pesquisas da Amazônia, Av. André Araújo, 2936, Petrópolis, 69067-375 Manaus, AM, Brazil
Manuscript received on April 2, 2019; accepted for publication on May 3,2019
How to cite: HOPKINS MJG. 2019. Are we close to knowing the plant diversity of the Amazon? An Acad Bras Cienc
91: e20190396. DOI 10.1590/0001-3765201920190396.
Abstract: Amazonia is often cited as having the most diverse ora on the planet. However, the total
number of species of higher plants in the region has been largely a matter of guesswork. Some recent
publications have estimated the total number of species present, which indicate a lower overall diversity
than was estimated in the past. However, analysis of the sampling density across the region, and data
from various sources suggest that there may be reason why the recent gures may be considerable
underestimates. I believe that much more investment in extensive collecting of quality plant specimens is
needed to encounter the very large number of rare and local species that might never have been collected.
Unfortunately the tendencies of investment in botany, in terms of geography and types of project, suggest
that we will probably not be able to accurately assess the real diversity of the region.
Key words: diversity, Amazonia, species discovery, plants.
E-mail: mikehopkins44@gmail.com
ORCid: https://orcid.org/0000-0001-5473-2942
INTRODUCTION
In 1992 a project was funded to provide a list of
species and guide to the plants of the Adolfo Ducke
Forest Reserve on the outskirts of Manaus. The
reserve was selected because it was known as the
botanically best known area in Amazonia with over
7000 registered plant collections, and a little over
1000 species recorded over 40 years (Ribeiro et
al. 1994). However, after 5 years of taxonomically
directed collecting, the number of species known
for the reserve approximately doubled (Hopkins
2005), and at least 50 species new to science were
found. This raised the question of how many new
species would be found if projects similar to the
Ducke Flora were carried out in poorly known
areas in Amazonia?
The low level of collection density across
Amazonia is well documented. Estimates of average
collection density across the region are between
0.1 and 0.2 collection per km2. Furthermore, there
is a very strong tendency for collection density
to be high in very few localities, such as close to
larger cities (Nelson et al. 1990, Schulman et al.
2007), and consequently far lower in more distant
and more rural areas. If the collection density is
low, the chances are that many species will not
be represented in species lists, and that species
with limited distributions in areas not visited by
botanists will not have been collected.
Recently, there have been more systematic
attempts to list the total number of species present by
assembling the taxonomic data based on herbarium
collections (Flora do Brasil 2018, ter Steege et
al. 2016) and by using modeling to estimate total
species richness from the data obtained from forest
MICHAEL J.G. HOPKINS AMAZON PLANT DIVERSITY
An Acad Bras Cienc (2019) 91(Suppl. 3) e20190396 2 | 7
inventories (ter Steege et al. 2013). By extrapolating
the rank abundance curve of almost 5000 species
of trees in forest plots, a total of approximately
16,000 species of trees was estimated for the
Amazon Basin, of which approximately 6,000 of
these would have populations of less than 1000
individuals.
The continuing Brazilian Flora project (Flora
do Brasil 2018) is listing the ora of Brazil based
on documentation in the literature and/or specimens
preserved in collections. These estimates tend to
be lower. The total number of Angiosperms (not
only trees) listed for Amazonia (only Brazil) was
12,217 in 2015, 12,414 in 2015 and 12,848 in 2018
(Forzza et al. 2010; Brazil Flora Group; Flora do
Brasil 2018). Notably, the total ora of states in the
southern third of Brazil often had longer species
lists than much larger states on Amazonian Brazil.
Ter Steege et al. (2016) also published a list of
11,676 tree species in Amazonia based on data from
herbaria, a number which was heavily criticized by
a group of botanists (Cardoso et al. 2017) who re-
evaluated the list based on taxonomically veried
data to only 6,727 tree species (and a total of 14,003
angiosperm species for all of the Amazon Basin).
The question I address in outline here is: are the
estimates being published reasonable minimum (or
maximum) estimates of Amazonian plant diversity,
or are their reasons to believe that the tendencies
in the history of collecting activity in the region
might cause significant underestimation of the
total diversity? These comments are in line with
previous publications (Hopkins 2007, Milliken et
al. 2011) and presage my on-going research and of
my students.
WHAT SORTS OF INFORMATION
SUGGEST THAT MANY MORE SPECIES
MIGHT BE AS YET UNDESCRIBED?
The examples given here are largely based on data
from monographs used in Hopkins (2007) and
data from a large personal data set of Amazonia
collections assembled and continuously updated
as part of my research. Note that in the case of
plant specimens the concept of the duplicate
strongly aects the calculations. Most botanists
made several duplicates of their collections,
which are distributed to dierent herbaria, where
they may follow different paths in terms of
their databasing and identification. This dataset
reassembles the duplicates to collection level
by standardizing the collector name and number
and standardizing species names, correcting for
synonymy. Nevertheless, it is a work in progress
with continuous cleaning activity.
1) Data on collection frequency in herbaria.
While some species have been collected many
times, probably because they are relatively
conspicuous because they are widespread, locally
common, ower regularly etc., others have been
rarely collected. The tallest column in figure 1
(in this case for Sapotaceae, but the same is seen
in most species diverse families) is for species
collected on only a single occasion. With further
collecting activity, especially of the type employed
in the Ducke project, that is to say directed towards
collecting the rarer species, we would expect
the curve to move to the right, and new species,
previously uncollected, would appear on the left.
This is an example of a veil line. In this case, the
shape of the curve suggests unknown diversity
hidden beyond the left axis of the graph.
2) Sizes of species distributions.
Some species have wide geographic distributions,
while others are very restricted in where they occur.
The size of a species’ range may be the result of
a number of ecological factors, such as niche
requirements limiting their distribution by type of
soil, vegetation type, altitude or hydraulic regime.
Geographic or other factors might limit their current
distribution, as might other biotic factors such as
their pollinators, herbivores, or competitive species.
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However, our knowledge of their distributions
is also limited by collection intensity, adequacy
of taxonomic study and identication. A species
recorded as widespread might actually be several
closely related, difficult to distinguish species,
a species recorded rarely might be difficult to
identify, ower rarely or occur in areas historically
unvisited by collecting botanists.
Herbarium data, and data in large on-line
datasets, are of limited use for assessing plant
distributions in Amazonia. Only a small proportion
of records are georeferenced (typically 15-30%
in most sources), and many errors in these occur.
Auto georeferencing in Amazonia is dicult as the
location data is often vague, incorrectly typed, or
referenced to places which do not appear on maps.
General estimates based for example on centroids
of municipalities are dangerous to use as many
municipalities in Amazonia are enormous. And
also many collectors do not record this level when
collecting, or are frequently incorrect. Furthermore,
identication errors are very common in online and
herbarium databases.
The best source of available geographical
information on species’ ranges is found in botanical
taxonomic monographs in the style of Flora
Neotropica. In these the author can be relied upon
to have correctly identied the material examined,
and have made studious attempts to manually
estimate the collection localities. Using this data
(Figure 2), it can be seen that relatively few species
have widespread distributions (as measured by the
number of 1 by 1 latitude/longitude degree squares
they have been recorded from). In this case, the
most frequent case is to be recorded from a single
degree square. This indicates that most species
of plants in Amazonia are not widely distributed,
but occur only very locally. Given that much of
Amazonia has not been botanically investigated,
this again suggests that there is another veil line
here where many species that happen to occur in
areas unvisited by botanists have yet to be collected.
3) Frequency in study plots.
Data from study plots where all plants above a
certain size are cataloged and identified should
indicate the degree of rarity or commonness
locally. There are a number of practical problems
Figure 1 - Frequency of occurrence of specimens of species mapped in monographs (Hopkins 2007).
MICHAEL J.G. HOPKINS AMAZON PLANT DIVERSITY
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in using this data, mostly associated with
identification. Even in herbaria, identifiers of
collections with owers and/or fruits often make
mistakes, and experience in many herbaria shows
that we can expect 20-45% of specimens to bear
an incorrect identication. Field identications are
even more dicult because the plants often lack
flowers or fruits on which taxonomic botanists
principally base their identification clues and
the identications are generally made by people
without detailed experience of the groups being
identied. Identication guides are generally not
available and using existing ones (such as Ribeiro
et al. 1999) is likely to cause identication errors in
areas distant from where it was researched. We can
therefore expect that rarer, and/or taxonomically
little-known species will be harder to identify, and
similar species (such as morphologically similar
congeneric species in hyper diverse genera) will
tend to be grouped. In the Ducke Reserve, we can
have more confidence in identifications and the
unpublished data from a forest inventory there
(Fig. 3 in Milliken et al. 2011) shows that the most
common pattern in 56 ha is to be represented by a
single individual. Again there is a veil line on the
left axis, with many species which were not found
in the inventory plots not appearing in this graph.
4) Taxonomic discovery curves.
With more knowledge of a regional flora,
especially with more collecting events, we will
gradually get closer to knowing the total number
of species that occur there. A curve of the number
of species known over time should be asymptotic,
gradually approaching the total number of species.
However, such curves in Amazonia do not t well
to an asymptotic curve. For example, the curve
for species discovery curve for Sapotaceae in
Amazonia (Figure 3) shows a more logarithmic
curve, much inuenced by taxonomic treatments
such as those by Pennington 1990, 2006) where
he described many species, mostly based on
recent collections. In this case the veil line is to
the right, with potentially more species to be found
in the future, but this obviously depends on more
collections being made.
Each of these analyses indicates that there are
certainly more species to be found in Amazonia.
Figure 2 - Frequency of area of occurrence for species of Sapotaceae (data from Pennington 1990).
MICHAEL J.G. HOPKINS AMAZON PLANT DIVERSITY
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But how many? Only a few or a very large
number? If we combine these analyses, I believe
it is clear that if we were able to make many more
collections in areas unvisited or only supercially
visited by botanists, many species with limited
distributions would be found. If we were able to
make collections over longer periods of time, the
locally rarer species would be more likely to be
collected in ower and fruit, and thus would be
described. Given that the data suggests that most
species are locally distributed, locally rare, the
combination of the diversity behind the veil lines
suggests that there is an enormous number of rare
species to be found, many more than predicted in
recent publications.
An interesting question is whether Amazonia
is intrinsically dierent from other areas in terms
of its record in taxonomic discovery. Using data
from all Brazilian species, and charting the rate of
accumulation of botanical knowledge by region
(percent of species known over time, based on the
date of publication of the earliest synonym) shows
a dierence in form between Amazonian Brazil
and the four other regions. It is dicult to compare
the ve regions as the point at which a region is
close to a 100% catalog of its species is dicult to
estimate. But a possible proxy for comparing the
taxonomic situation is to measure the dierence
(in years) between the dates at which each region
achieved 50% of the taxonomic knowledge that
we have today. Doing this (Figure 4) indicates
that Amazonia is, by this conservative measure,
65 years behind all the other regions of Brazil.
Repeating this analysis at state level (Figure 5)
shows a strong negative tendency from the south
east to the north west, with all the Amazonian states
far behind the southern and northeastern states in
terms of discovery of their oras.
WILL WE DISCOVER THESE
UNKNOWN SPECIES?
The only possible means to discover the missing
biodiversity is through intensive collections,
especially in areas distant from cities. Given the size
of Amazonia, the nancial and administrative costs
of undertaking long-term research is very high.
Furthermore, basic, explorative research and the
Figure 3 - Species discovery curve for Amazonian Sapotaceae.
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Figure 4 - Species discovery curves for Angiosperm species for 5 geograc regions of Brazil,
indicating when the 50% of current knowledge point was reached.
Figure 5 - Relative date of 50% knowledge for Brazilian states. Red columns in years
behind the average for Brazil (maximum Amazonas state -66 years) Blue columns ahead
of the average (maximum 17 years - several northeast states).
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investment in collections and taxonomic research
is no longer prioritized. Collecting expeditions
are considered “old-fashioned” if not linked with
innovation, development, or ecological modeling
on a global scale. Unfortunately the consequences
for conservation, modeling and development -
based on inadequate taxonomy and consequently
erroneous identifications - are an “inconvenient
truth” for funding decision makers.
CAN AMAZONIA “CATCH UP”?
Another aspect to the botanical problems in
Amazonia is the unequal geographical distribution
of resources, both human and nancial, in Brazil.
Although Amazonia accounts for more than half of
the territory of Brazil, recent specically botanical
programs have allocated only between 5 and 10%
of the resources to Amazonia, with the vast majority
being allocated to three states in the south east, São
Paulo, Rio de Janeiro and Minas Gerais. Human
resources are also greatly skewed in the same way.
If it is thought to be important to have access
to the genomes of Amazonia plants, or to know
the correct identity of plants being exploited, or
to know the real numbers of species present in any
ecosystem, I think it is clear that there needs to be
a massive reorganizing of resources within Brazil,
with a program of “biodiversity prospection” on
a continental scale. Studying only the currently
known species will result in poor planning, poor
conservation and missed opportunities.
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